diff --git a/src/AstGen.zig b/src/AstGen.zig
index b613a6b677..f709751fde 100644
--- a/src/AstGen.zig
+++ b/src/AstGen.zig
@@ -1753,7 +1753,6 @@ fn structInitExpr(
         const sfba_allocator = sfba.get();
 
         var duplicate_names = std.AutoArrayHashMap(Zir.NullTerminatedString, ArrayListUnmanaged(Ast.TokenIndex)).init(sfba_allocator);
-        defer duplicate_names.deinit();
         try duplicate_names.ensureTotalCapacity(@intCast(struct_init.ast.fields.len));
 
         // When there aren't errors, use this to avoid a second iteration.
@@ -1783,12 +1782,14 @@ fn structInitExpr(
                     var error_notes = std.ArrayList(u32).init(astgen.arena);
 
                     for (record.items[1..]) |duplicate| {
-                        try error_notes.append(try astgen.errNoteTok(duplicate, "other field here", .{}));
+                        try error_notes.append(try astgen.errNoteTok(duplicate, "duplicate name here", .{}));
                     }
 
+                    try error_notes.append(try astgen.errNoteNode(node, "struct declared here", .{}));
+
                     try astgen.appendErrorTokNotes(
                         record.items[0],
-                        "duplicate field",
+                        "duplicate struct field name",
                         .{},
                         error_notes.items,
                     );
@@ -1815,9 +1816,10 @@ fn structInitExpr(
     switch (ri.rl) {
         .none => return structInitExprAnon(gz, scope, node, struct_init),
         .discard => {
-            // Even if discarding we must perform an anonymous init to check for duplicate field names.
-            // TODO: should duplicate field names be caught in AstGen?
-            _ = try structInitExprAnon(gz, scope, node, struct_init);
+            // Even if discarding we must perform side-effects.
+            for (struct_init.ast.fields) |field_init| {
+                _ = try expr(gz, scope, .{ .rl = .discard }, field_init);
+            }
             return .void_value;
         },
         .ref => {
@@ -5101,15 +5103,15 @@ fn structDeclInner(
                 var error_notes = std.ArrayList(u32).init(astgen.arena);
 
                 for (record.items[1..]) |duplicate| {
-                    try error_notes.append(try astgen.errNoteTok(duplicate, "other field here", .{}));
+                    try error_notes.append(try astgen.errNoteTok(duplicate, "duplicate field here", .{}));
                 }
 
                 try error_notes.append(try astgen.errNoteNode(node, "struct declared here", .{}));
 
                 try astgen.appendErrorTokNotes(
                     record.items[0],
-                    "duplicate struct field: '{s}'",
-                    .{try astgen.identifierTokenString(record.items[0])},
+                    "duplicate struct field name",
+                    .{},
                     error_notes.items,
                 );
             }
@@ -5118,8 +5120,6 @@ fn structDeclInner(
         return error.AnalysisFail;
     }
 
-    duplicate_names.deinit();
-
     try gz.setStruct(decl_inst, .{
         .src_node = node,
         .layout = layout,
@@ -5211,6 +5211,15 @@ fn unionDeclInner(
     var wip_members = try WipMembers.init(gpa, &astgen.scratch, decl_count, field_count, bits_per_field, max_field_size);
     defer wip_members.deinit();
 
+    var sfba = std.heap.stackFallback(256, astgen.arena);
+    const sfba_allocator = sfba.get();
+
+    var duplicate_names = std.AutoArrayHashMap(Zir.NullTerminatedString, std.ArrayListUnmanaged(Ast.TokenIndex)).init(sfba_allocator);
+    try duplicate_names.ensureTotalCapacity(field_count);
+
+    // When there aren't errors, use this to avoid a second iteration.
+    var any_duplicate = false;
+
     for (members) |member_node| {
         var member = switch (try containerMember(&block_scope, &namespace.base, &wip_members, member_node)) {
             .decl => continue,
@@ -5227,6 +5236,16 @@ fn unionDeclInner(
         const field_name = try astgen.identAsString(member.ast.main_token);
         wip_members.appendToField(@intFromEnum(field_name));
 
+        const gop = try duplicate_names.getOrPut(field_name);
+
+        if (gop.found_existing) {
+            try gop.value_ptr.append(sfba_allocator, member.ast.main_token);
+            any_duplicate = true;
+        } else {
+            gop.value_ptr.* = .{};
+            try gop.value_ptr.append(sfba_allocator, member.ast.main_token);
+        }
+
         const doc_comment_index = try astgen.docCommentAsString(member.firstToken());
         wip_members.appendToField(@intFromEnum(doc_comment_index));
 
@@ -5281,6 +5300,32 @@ fn unionDeclInner(
         }
     }
 
+    if (any_duplicate) {
+        var it = duplicate_names.iterator();
+
+        while (it.next()) |entry| {
+            const record = entry.value_ptr.*;
+            if (record.items.len > 1) {
+                var error_notes = std.ArrayList(u32).init(astgen.arena);
+
+                for (record.items[1..]) |duplicate| {
+                    try error_notes.append(try astgen.errNoteTok(duplicate, "duplicate field here", .{}));
+                }
+
+                try error_notes.append(try astgen.errNoteNode(node, "union declared here", .{}));
+
+                try astgen.appendErrorTokNotes(
+                    record.items[0],
+                    "duplicate union field name",
+                    .{},
+                    error_notes.items,
+                );
+            }
+        }
+
+        return error.AnalysisFail;
+    }
+
     if (!block_scope.isEmpty()) {
         _ = try block_scope.addBreak(.break_inline, decl_inst, .void_value);
     }
@@ -5490,6 +5535,15 @@ fn containerDecl(
             var wip_members = try WipMembers.init(gpa, &astgen.scratch, @intCast(counts.decls), @intCast(counts.total_fields), bits_per_field, max_field_size);
             defer wip_members.deinit();
 
+            var sfba = std.heap.stackFallback(256, astgen.arena);
+            const sfba_allocator = sfba.get();
+
+            var duplicate_names = std.AutoArrayHashMap(Zir.NullTerminatedString, std.ArrayListUnmanaged(Ast.TokenIndex)).init(sfba_allocator);
+            try duplicate_names.ensureTotalCapacity(counts.total_fields);
+
+            // When there aren't errors, use this to avoid a second iteration.
+            var any_duplicate = false;
+
             for (container_decl.ast.members) |member_node| {
                 if (member_node == counts.nonexhaustive_node)
                     continue;
@@ -5506,6 +5560,16 @@ fn containerDecl(
                 const field_name = try astgen.identAsString(member.ast.main_token);
                 wip_members.appendToField(@intFromEnum(field_name));
 
+                const gop = try duplicate_names.getOrPut(field_name);
+
+                if (gop.found_existing) {
+                    try gop.value_ptr.append(sfba_allocator, member.ast.main_token);
+                    any_duplicate = true;
+                } else {
+                    gop.value_ptr.* = .{};
+                    try gop.value_ptr.append(sfba_allocator, member.ast.main_token);
+                }
+
                 const doc_comment_index = try astgen.docCommentAsString(member.firstToken());
                 wip_members.appendToField(@intFromEnum(doc_comment_index));
 
@@ -5533,6 +5597,32 @@ fn containerDecl(
                 }
             }
 
+            if (any_duplicate) {
+                var it = duplicate_names.iterator();
+
+                while (it.next()) |entry| {
+                    const record = entry.value_ptr.*;
+                    if (record.items.len > 1) {
+                        var error_notes = std.ArrayList(u32).init(astgen.arena);
+
+                        for (record.items[1..]) |duplicate| {
+                            try error_notes.append(try astgen.errNoteTok(duplicate, "duplicate field here", .{}));
+                        }
+
+                        try error_notes.append(try astgen.errNoteNode(node, "enum declared here", .{}));
+
+                        try astgen.appendErrorTokNotes(
+                            record.items[0],
+                            "duplicate enum field name",
+                            .{},
+                            error_notes.items,
+                        );
+                    }
+                }
+
+                return error.AnalysisFail;
+            }
+
             if (!block_scope.isEmpty()) {
                 _ = try block_scope.addBreak(.break_inline, decl_inst, .void_value);
             }
diff --git a/src/Sema.zig b/src/Sema.zig
index a38da0adef..96be1a441f 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -3046,23 +3046,10 @@ fn zirEnumDecl(
 
         const field_name_index: Zir.NullTerminatedString = @enumFromInt(sema.code.extra[extra_index]);
         const field_name_zir = sema.code.nullTerminatedString(field_name_index);
-        extra_index += 1;
-
-        // doc comment
-        extra_index += 1;
+        extra_index += 2; // field name, doc comment
 
         const field_name = try mod.intern_pool.getOrPutString(gpa, field_name_zir);
-        if (incomplete_enum.addFieldName(&mod.intern_pool, field_name)) |other_index| {
-            const field_src = mod.fieldSrcLoc(new_decl_index, .{ .index = field_i }).lazy;
-            const other_field_src = mod.fieldSrcLoc(new_decl_index, .{ .index = other_index }).lazy;
-            const msg = msg: {
-                const msg = try sema.errMsg(block, field_src, "duplicate enum field '{s}'", .{field_name_zir});
-                errdefer msg.destroy(gpa);
-                try sema.errNote(block, other_field_src, msg, "other field here", .{});
-                break :msg msg;
-            };
-            return sema.failWithOwnedErrorMsg(block, msg);
-        }
+        assert(incomplete_enum.addFieldName(&mod.intern_pool, field_name) == null);
 
         const tag_overflow = if (has_tag_value) overflow: {
             const tag_val_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
@@ -21732,7 +21719,7 @@ fn reifyStruct(
             }
         } else if (struct_type.addFieldName(ip, field_name)) |prev_index| {
             _ = prev_index; // TODO: better source location
-            return sema.fail(block, src, "duplicate struct field {}", .{field_name.fmt(ip)});
+            return sema.fail(block, src, "duplicate struct field name {}", .{field_name.fmt(ip)});
         }
 
         const field_ty = type_val.toType();
@@ -36284,7 +36271,6 @@ fn semaStructFields(
     const zir = mod.namespacePtr(namespace_index).file_scope.zir;
     const zir_index = struct_type.zir_index;
 
-    const src = LazySrcLoc.nodeOffset(0);
     const fields_len, const small, var extra_index = structZirInfo(zir, zir_index);
 
     if (fields_len == 0) switch (struct_type.layout) {
@@ -36384,19 +36370,7 @@ fn semaStructFields(
             // This string needs to outlive the ZIR code.
             if (opt_field_name_zir) |field_name_zir| {
                 const field_name = try ip.getOrPutString(gpa, field_name_zir);
-                if (struct_type.addFieldName(ip, field_name)) |other_index| {
-                    const msg = msg: {
-                        const field_src = mod.fieldSrcLoc(decl_index, .{ .index = field_i }).lazy;
-                        const msg = try sema.errMsg(&block_scope, field_src, "duplicate struct field: '{}'", .{field_name.fmt(ip)});
-                        errdefer msg.destroy(gpa);
-
-                        const prev_field_src = mod.fieldSrcLoc(decl_index, .{ .index = other_index });
-                        try mod.errNoteNonLazy(prev_field_src, msg, "other field here", .{});
-                        try sema.errNote(&block_scope, src, msg, "struct declared here", .{});
-                        break :msg msg;
-                    };
-                    return sema.failWithOwnedErrorMsg(&block_scope, msg);
-                }
+                assert(struct_type.addFieldName(ip, field_name) == null);
             }
 
             if (has_align) {
@@ -36840,12 +36814,10 @@ fn semaUnionFields(mod: *Module, arena: Allocator, union_type: InternPool.Key.Un
 
     var field_types: std.ArrayListUnmanaged(InternPool.Index) = .{};
     var field_aligns: std.ArrayListUnmanaged(InternPool.Alignment) = .{};
-    var field_name_table: std.AutoArrayHashMapUnmanaged(InternPool.NullTerminatedString, void) = .{};
 
     try field_types.ensureTotalCapacityPrecise(sema.arena, fields_len);
     if (small.any_aligned_fields)
         try field_aligns.ensureTotalCapacityPrecise(sema.arena, fields_len);
-    try field_name_table.ensureTotalCapacity(sema.arena, fields_len);
 
     const bits_per_field = 4;
     const fields_per_u32 = 32 / bits_per_field;
@@ -36961,23 +36933,6 @@ fn semaUnionFields(mod: *Module, arena: Allocator, union_type: InternPool.Key.Un
             return error.GenericPoison;
         }
 
-        const gop = field_name_table.getOrPutAssumeCapacity(field_name);
-        if (gop.found_existing) {
-            const msg = msg: {
-                const field_src = mod.fieldSrcLoc(union_type.decl, .{ .index = field_i }).lazy;
-                const msg = try sema.errMsg(&block_scope, field_src, "duplicate union field: '{}'", .{
-                    field_name.fmt(ip),
-                });
-                errdefer msg.destroy(gpa);
-
-                const prev_field_src = mod.fieldSrcLoc(union_type.decl, .{ .index = gop.index }).lazy;
-                try mod.errNoteNonLazy(prev_field_src.toSrcLoc(decl, mod), msg, "other field here", .{});
-                try sema.errNote(&block_scope, src, msg, "union declared here", .{});
-                break :msg msg;
-            };
-            return sema.failWithOwnedErrorMsg(&block_scope, msg);
-        }
-
         if (explicit_tags_seen.len > 0) {
             const tag_info = ip.indexToKey(union_type.tagTypePtr(ip).*).enum_type;
             const enum_index = tag_info.nameIndex(ip, field_name) orelse {
diff --git a/test/cases/compile_errors/duplicate_enum_field.zig b/test/cases/compile_errors/duplicate_enum_field.zig
index ebf01f99a7..02738f1b37 100644
--- a/test/cases/compile_errors/duplicate_enum_field.zig
+++ b/test/cases/compile_errors/duplicate_enum_field.zig
@@ -12,5 +12,6 @@ export fn entry() void {
 // backend=stage2
 // target=native
 //
-// :3:5: error: duplicate enum field 'Bar'
-// :2:5: note: other field here
+// :2:5: error: duplicate enum field name
+// :3:5: note: duplicate field here
+// :1:13: note: enum declared here
diff --git a/test/cases/compile_errors/duplicate_field_in_anonymous_struct_literal.zig b/test/cases/compile_errors/duplicate_field_in_anonymous_struct_literal.zig
index ee81f72b1d..e1e220e346 100644
--- a/test/cases/compile_errors/duplicate_field_in_anonymous_struct_literal.zig
+++ b/test/cases/compile_errors/duplicate_field_in_anonymous_struct_literal.zig
@@ -14,5 +14,6 @@ export fn entry() void {
 // backend=stage2
 // target=native
 //
-// :4:14: error: duplicate field
-// :7:14: note: other field here
+// :4:14: error: duplicate struct field name
+// :7:14: note: duplicate name here
+// :3:19: note: struct declared here
diff --git a/test/cases/compile_errors/duplicate_field_in_discarded_anon_init.zig b/test/cases/compile_errors/duplicate_field_in_discarded_anon_init.zig
index ff1912d27b..913100f79b 100644
--- a/test/cases/compile_errors/duplicate_field_in_discarded_anon_init.zig
+++ b/test/cases/compile_errors/duplicate_field_in_discarded_anon_init.zig
@@ -6,5 +6,6 @@ pub export fn entry() void {
 // backend=stage2
 // target=native
 //
-// :2:13: error: duplicate field
-// :2:21: note: other field here
+// :2:13: error: duplicate struct field name
+// :2:21: note: duplicate name here
+// :2:10: note: struct declared here
diff --git a/test/cases/compile_errors/duplicate_field_in_struct_value_expression.zig b/test/cases/compile_errors/duplicate_field_in_struct_value_expression.zig
index e52f835146..b0f656b3c4 100644
--- a/test/cases/compile_errors/duplicate_field_in_struct_value_expression.zig
+++ b/test/cases/compile_errors/duplicate_field_in_struct_value_expression.zig
@@ -17,5 +17,6 @@ export fn f() void {
 // backend=stage2
 // target=native
 //
-// :8:10: error: duplicate field
-// :11:10: note: other field here
+// :8:10: error: duplicate struct field name
+// :11:10: note: duplicate name here
+// :7:16: note: struct declared here
diff --git a/test/cases/compile_errors/duplicate_struct_field.zig b/test/cases/compile_errors/duplicate_struct_field.zig
index 61340a423e..954ed24e92 100644
--- a/test/cases/compile_errors/duplicate_struct_field.zig
+++ b/test/cases/compile_errors/duplicate_struct_field.zig
@@ -24,10 +24,10 @@ export fn b() void {
 // backend=stage2
 // target=native
 //
-// :2:5: error: duplicate struct field: 'Bar'
-// :3:5: note: other field here
+// :2:5: error: duplicate struct field name
+// :3:5: note: duplicate field here
 // :1:13: note: struct declared here
-// :7:5: error: duplicate struct field: 'a'
-// :9:5: note: other field here
-// :10:5: note: other field here
+// :7:5: error: duplicate struct field name
+// :9:5: note: duplicate field here
+// :10:5: note: duplicate field here
 // :6:11: note: struct declared here
diff --git a/test/cases/compile_errors/duplicate_union_field.zig b/test/cases/compile_errors/duplicate_union_field.zig
index 6a0265dd02..b57842c1f7 100644
--- a/test/cases/compile_errors/duplicate_union_field.zig
+++ b/test/cases/compile_errors/duplicate_union_field.zig
@@ -11,6 +11,6 @@ export fn entry() void {
 // backend=stage2
 // target=native
 //
-// :3:5: error: duplicate union field: 'Bar'
-// :2:5: note: other field here
+// :2:5: error: duplicate union field name
+// :3:5: note: duplicate field here
 // :1:13: note: union declared here
diff --git a/test/cases/compile_errors/error_in_struct_initializer_doesnt_crash_the_compiler.zig b/test/cases/compile_errors/error_in_struct_initializer_doesnt_crash_the_compiler.zig
index 515ac855ce..ea799c561a 100644
--- a/test/cases/compile_errors/error_in_struct_initializer_doesnt_crash_the_compiler.zig
+++ b/test/cases/compile_errors/error_in_struct_initializer_doesnt_crash_the_compiler.zig
@@ -11,6 +11,6 @@ pub export fn entry() void {
 // backend=stage2
 // target=native
 //
-// :3:9: error: duplicate struct field: 'e'
-// :4:9: note: other field here
+// :3:9: error: duplicate struct field name
+// :4:9: note: duplicate field here
 // :2:22: note: struct declared here
diff --git a/test/cases/compile_errors/struct_duplicate_field_name.zig b/test/cases/compile_errors/struct_duplicate_field_name.zig
index d19e94b9d2..057083c3cb 100644
--- a/test/cases/compile_errors/struct_duplicate_field_name.zig
+++ b/test/cases/compile_errors/struct_duplicate_field_name.zig
@@ -11,6 +11,6 @@ export fn entry() void {
 // error
 // target=native
 //
-// :2:5: error: duplicate struct field: 'foo'
-// :3:5: note: other field here
+// :2:5: error: duplicate struct field name
+// :3:5: note: duplicate field here
 // :1:11: note: struct declared here
diff --git a/test/cases/compile_errors/union_duplicate_enum_field.zig b/test/cases/compile_errors/union_duplicate_enum_field.zig
index 6a5fafbb25..21c307755b 100644
--- a/test/cases/compile_errors/union_duplicate_enum_field.zig
+++ b/test/cases/compile_errors/union_duplicate_enum_field.zig
@@ -12,6 +12,6 @@ export fn foo() void {
 // error
 // target=native
 //
-// :4:5: error: duplicate union field: 'a'
-// :3:5: note: other field here
+// :3:5: error: duplicate union field name
+// :4:5: note: duplicate field here
 // :2:11: note: union declared here
diff --git a/test/cases/compile_errors/union_duplicate_field_definition.zig b/test/cases/compile_errors/union_duplicate_field_definition.zig
index 7993f27141..e0866964eb 100644
--- a/test/cases/compile_errors/union_duplicate_field_definition.zig
+++ b/test/cases/compile_errors/union_duplicate_field_definition.zig
@@ -11,6 +11,6 @@ export fn entry() void {
 // error
 // target=native
 //
-// :3:5: error: duplicate union field: 'foo'
-// :2:5: note: other field here
+// :2:5: error: duplicate union field name
+// :3:5: note: duplicate field here
 // :1:11: note: union declared here
diff --git a/test/cbe.zig b/test/cbe.zig
index 26724a1df0..35c2d8e8f9 100644
--- a/test/cbe.zig
+++ b/test/cbe.zig
@@ -507,8 +507,9 @@ pub fn addCases(ctx: *Cases, b: *std.Build) !void {
             \\    return p.y - p.x - p.x;
             \\}
         , &.{
-            ":4:10: error: duplicate field",
-            ":6:10: note: other field here",
+            ":4:10: error: duplicate struct field name",
+            ":6:10: note: duplicate name here",
+            ":3:21: note: struct declared here",
         });
         case.addError(
             \\const Point = struct { x: i32, y: i32 };
@@ -722,8 +723,9 @@ pub fn addCases(ctx: *Cases, b: *std.Build) !void {
             \\    _ = E1.a;
             \\}
         , &.{
-            ":1:28: error: duplicate enum field 'b'",
-            ":1:22: note: other field here",
+            ":1:22: error: duplicate enum field name",
+            ":1:28: note: duplicate field here",
+            ":1:12: note: enum declared here",
         });
 
         case.addError(