diff --git a/src/all_types.hpp b/src/all_types.hpp
index daf37e5956..f6342cb8a0 100644
--- a/src/all_types.hpp
+++ b/src/all_types.hpp
@@ -1129,6 +1129,7 @@ enum BuiltinFnId {
     BuiltinFnIdCmpExchange,
     BuiltinFnIdFence,
     BuiltinFnIdDivExact,
+    BuiltinFnIdTruncate,
 };
 
 struct BuiltinFnEntry {
diff --git a/src/analyze.cpp b/src/analyze.cpp
index 133cbf47fa..233bc4e7b2 100644
--- a/src/analyze.cpp
+++ b/src/analyze.cpp
@@ -4686,6 +4686,44 @@ static TypeTableEntry *analyze_div_exact(CodeGen *g, ImportTableEntry *import,
     }
 }
 
+static TypeTableEntry *analyze_truncate(CodeGen *g, ImportTableEntry *import,
+        BlockContext *context, AstNode *node)
+{
+    assert(node->type == NodeTypeFnCallExpr);
+
+    AstNode **op1 = &node->data.fn_call_expr.params.at(0);
+    AstNode **op2 = &node->data.fn_call_expr.params.at(1);
+
+    TypeTableEntry *dest_type = analyze_type_expr(g, import, context, *op1);
+    TypeTableEntry *src_type = analyze_expression(g, import, context, nullptr, *op2);
+
+    if (dest_type->id == TypeTableEntryIdInvalid || src_type->id == TypeTableEntryIdInvalid) {
+        return g->builtin_types.entry_invalid;
+    } else if (dest_type->id != TypeTableEntryIdInt) {
+        add_node_error(g, *op1,
+                buf_sprintf("expected integer type, got '%s'", buf_ptr(&dest_type->name)));
+        return g->builtin_types.entry_invalid;
+    } else if (src_type->id != TypeTableEntryIdInt) {
+        add_node_error(g, *op2,
+                buf_sprintf("expected integer type, got '%s'", buf_ptr(&src_type->name)));
+        return g->builtin_types.entry_invalid;
+    } else if (src_type->data.integral.is_signed != dest_type->data.integral.is_signed) {
+        const char *sign_str = dest_type->data.integral.is_signed ? "signed" : "unsigned";
+        add_node_error(g, *op2,
+                buf_sprintf("expected %s integer type, got '%s'", sign_str, buf_ptr(&src_type->name)));
+        return g->builtin_types.entry_invalid;
+    } else if (src_type->data.integral.bit_count <= dest_type->data.integral.bit_count) {
+        add_node_error(g, *op2,
+                buf_sprintf("type '%s' has same or fewer bits than destination type '%s'",
+                    buf_ptr(&src_type->name), buf_ptr(&dest_type->name)));
+        return g->builtin_types.entry_invalid;
+    }
+
+    // TODO const expr eval
+
+    return dest_type;
+}
+
 static TypeTableEntry *analyze_builtin_fn_call_expr(CodeGen *g, ImportTableEntry *import, BlockContext *context,
         TypeTableEntry *expected_type, AstNode *node)
 {
@@ -5028,6 +5066,8 @@ static TypeTableEntry *analyze_builtin_fn_call_expr(CodeGen *g, ImportTableEntry
             return analyze_fence(g, import, context, node);
         case BuiltinFnIdDivExact:
             return analyze_div_exact(g, import, context, node);
+        case BuiltinFnIdTruncate:
+            return analyze_truncate(g, import, context, node);
     }
     zig_unreachable();
 }
diff --git a/src/codegen.cpp b/src/codegen.cpp
index 8163cf9fc9..13f0c9eee0 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -473,6 +473,18 @@ static LLVMValueRef gen_div_exact(CodeGen *g, AstNode *node) {
     return gen_div(g, node, op1_val, op2_val, get_expr_type(op1_node), true);
 }
 
+static LLVMValueRef gen_truncate(CodeGen *g, AstNode *node) {
+    assert(node->type == NodeTypeFnCallExpr);
+
+    TypeTableEntry *dest_type = get_type_for_type_node(node->data.fn_call_expr.params.at(0));
+    AstNode *src_node = node->data.fn_call_expr.params.at(1);
+
+    LLVMValueRef src_val = gen_expr(g, src_node);
+
+    set_debug_source_node(g, node);
+    return LLVMBuildTrunc(g->builder, src_val, dest_type->type_ref, "");
+}
+
 static LLVMValueRef gen_shl_with_overflow(CodeGen *g, AstNode *node) {
     assert(node->type == NodeTypeFnCallExpr);
 
@@ -661,6 +673,8 @@ static LLVMValueRef gen_builtin_fn_call_expr(CodeGen *g, AstNode *node) {
             return gen_fence(g, node);
         case BuiltinFnIdDivExact:
             return gen_div_exact(g, node);
+        case BuiltinFnIdTruncate:
+            return gen_truncate(g, node);
     }
     zig_unreachable();
 }
@@ -729,6 +743,24 @@ static LLVMValueRef gen_widen_or_shorten(CodeGen *g, AstNode *source_node, TypeT
         zig_unreachable();
     }
 
+    if (actual_bits >= wanted_bits && actual_type->id == TypeTableEntryIdInt &&
+        !wanted_type->data.integral.is_signed && actual_type->data.integral.is_signed &&
+        want_debug_safety(g, source_node))
+    {
+        set_debug_source_node(g, source_node);
+        LLVMValueRef zero = LLVMConstNull(actual_type->type_ref);
+        LLVMValueRef ok_bit = LLVMBuildICmp(g->builder, LLVMIntSGE, expr_val, zero, "");
+
+        LLVMBasicBlockRef ok_block = LLVMAppendBasicBlock(g->cur_fn->fn_value, "SignCastOk");
+        LLVMBasicBlockRef fail_block = LLVMAppendBasicBlock(g->cur_fn->fn_value, "SignCastFail");
+        LLVMBuildCondBr(g->builder, ok_bit, ok_block, fail_block);
+
+        LLVMPositionBuilderAtEnd(g->builder, fail_block);
+        gen_debug_safety_crash(g);
+
+        LLVMPositionBuilderAtEnd(g->builder, ok_block);
+    }
+
     if (actual_bits == wanted_bits) {
         return expr_val;
     } else if (actual_bits < wanted_bits) {
@@ -752,7 +784,26 @@ static LLVMValueRef gen_widen_or_shorten(CodeGen *g, AstNode *source_node, TypeT
             return LLVMBuildFPTrunc(g->builder, expr_val, wanted_type->type_ref, "");
         } else if (actual_type->id == TypeTableEntryIdInt) {
             set_debug_source_node(g, source_node);
-            return LLVMBuildTrunc(g->builder, expr_val, wanted_type->type_ref, "");
+            LLVMValueRef trunc_val = LLVMBuildTrunc(g->builder, expr_val, wanted_type->type_ref, "");
+            if (!want_debug_safety(g, source_node)) {
+                return trunc_val;
+            }
+            LLVMValueRef orig_val;
+            if (actual_type->data.integral.is_signed) {
+                orig_val = LLVMBuildSExt(g->builder, trunc_val, actual_type->type_ref, "");
+            } else {
+                orig_val = LLVMBuildZExt(g->builder, trunc_val, actual_type->type_ref, "");
+            }
+            LLVMValueRef ok_bit = LLVMBuildICmp(g->builder, LLVMIntEQ, expr_val, orig_val, "");
+            LLVMBasicBlockRef ok_block = LLVMAppendBasicBlock(g->cur_fn->fn_value, "CastShortenOk");
+            LLVMBasicBlockRef fail_block = LLVMAppendBasicBlock(g->cur_fn->fn_value, "CastShortenFail");
+            LLVMBuildCondBr(g->builder, ok_bit, ok_block, fail_block);
+
+            LLVMPositionBuilderAtEnd(g->builder, fail_block);
+            gen_debug_safety_crash(g);
+
+            LLVMPositionBuilderAtEnd(g->builder, ok_block);
+            return trunc_val;
         } else {
             zig_unreachable();
         }
@@ -4568,6 +4619,7 @@ static void define_builtin_fns(CodeGen *g) {
     create_builtin_fn_with_arg_count(g, BuiltinFnIdCmpExchange, "cmpxchg", 5);
     create_builtin_fn_with_arg_count(g, BuiltinFnIdFence, "fence", 1);
     create_builtin_fn_with_arg_count(g, BuiltinFnIdDivExact, "div_exact", 2);
+    create_builtin_fn_with_arg_count(g, BuiltinFnIdTruncate, "truncate", 2);
 }
 
 static void init(CodeGen *g, Buf *source_path) {
diff --git a/src/eval.cpp b/src/eval.cpp
index b31cc47daa..4499b8529f 100644
--- a/src/eval.cpp
+++ b/src/eval.cpp
@@ -827,6 +827,7 @@ static bool eval_fn_call_builtin(EvalFn *ef, AstNode *node, ConstExprValue *out_
         case BuiltinFnIdErrName:
         case BuiltinFnIdEmbedFile:
         case BuiltinFnIdCmpExchange:
+        case BuiltinFnIdTruncate:
             zig_panic("TODO");
         case BuiltinFnIdBreakpoint:
         case BuiltinFnIdInvalid:
diff --git a/std/rand.zig b/std/rand.zig
index b7bf8be04b..725863d244 100644
--- a/std/rand.zig
+++ b/std/rand.zig
@@ -15,7 +15,7 @@ pub struct Rand {
         var i : isize = 1;
         var prev_value: u64w = seed;
         while (i < ARRAY_SIZE; i += 1) {
-            r.array[i] = u32((prev_value ^ (prev_value << 30)) * 0x6c078965 + u64w(i));
+            r.array[i] = @truncate(u32, (prev_value ^ (prev_value << 30)) * 0x6c078965 + u64w(i));
             prev_value = r.array[i];
         }
         return r;
diff --git a/test/run_tests.cpp b/test/run_tests.cpp
index f4f958b911..aee5fe17fe 100644
--- a/test/run_tests.cpp
+++ b/test/run_tests.cpp
@@ -1368,6 +1368,20 @@ fn add(x: i8w, y: i32) {
 }
     )SOURCE", 1, ".tmp_source.zig:3:17: error: incompatible types: 'i8w' and 'i32'");
 
+    add_compile_fail_case("truncate sign mismatch", R"SOURCE(
+fn f() {
+    const x: u32 = 10;
+    @truncate(i8, x);
+}
+    )SOURCE", 1, ".tmp_source.zig:4:19: error: expected signed integer type, got 'u32'");
+
+    add_compile_fail_case("truncate same bit count", R"SOURCE(
+fn f() {
+    const x: i8 = 10;
+    @truncate(i8, x);
+}
+    )SOURCE", 1, ".tmp_source.zig:4:19: error: type 'i8' has same or fewer bits than destination type 'i8'");
+
 }
 
 //////////////////////////////////////////////////////////////////////////////
@@ -1476,6 +1490,26 @@ fn widen_slice(slice: []u8) -> []i32 {
 }
     )SOURCE");
 
+    add_debug_safety_case("value does not fit in shortening cast", R"SOURCE(
+pub fn main(args: [][]u8) -> %void {
+    shorten_cast(200);
+}
+#static_eval_enable(false)
+fn shorten_cast(x: i32) -> i8 {
+    i8(x)
+}
+    )SOURCE");
+
+    add_debug_safety_case("signed integer not fitting in cast to unsigned integer", R"SOURCE(
+pub fn main(args: [][]u8) -> %void {
+    unsigned_cast(-10);
+}
+#static_eval_enable(false)
+fn unsigned_cast(x: i32) -> u32 {
+    u32(x)
+}
+    )SOURCE");
+
 }
 
 //////////////////////////////////////////////////////////////////////////////
diff --git a/test/self_hosted.zig b/test/self_hosted.zig
index 99ae4800de..ab5fde33a9 100644
--- a/test/self_hosted.zig
+++ b/test/self_hosted.zig
@@ -1631,3 +1631,12 @@ struct SillyStruct {
 const here_is_a_null_literal = SillyStruct {
     .context = null,
 };
+
+#attribute("test")
+fn truncate() {
+    assert(test_truncate(0x10fd) == 0xfd);
+}
+#static_eval_enable(false)
+fn test_truncate(x: u32) -> u8 {
+    @truncate(u8, x)
+}