diff --git a/lib/std/zig/parser_test.zig b/lib/std/zig/parser_test.zig
index 4ec527fd6c..2b9e3fb03c 100644
--- a/lib/std/zig/parser_test.zig
+++ b/lib/std/zig/parser_test.zig
@@ -4190,6 +4190,17 @@ test "zig fmt: function with labeled block as return type" {
     );
 }
 
+test "zig fmt: extern function with missing param name" {
+    try testCanonical(
+        \\extern fn a(
+        \\    *b,
+        \\    c: *d,
+        \\) e;
+        \\extern fn f(*g, h: *i) j;
+        \\
+    );
+}
+
 test "zig fmt: line comment after multiline single expr if statement with multiline string" {
     try testCanonical(
         \\test {
diff --git a/lib/std/zig/render.zig b/lib/std/zig/render.zig
index 673a05f8e6..e12f7bc733 100644
--- a/lib/std/zig/render.zig
+++ b/lib/std/zig/render.zig
@@ -1449,9 +1449,11 @@ fn renderFnProto(gpa: *Allocator, ais: *Ais, tree: ast.Tree, fn_proto: ast.full.
                     continue;
                 },
                 .r_paren => break,
-                else => unreachable,
+                else => {}, // Parameter type without a name.
             }
-            if (token_tags[last_param_token] == .identifier) {
+            if (token_tags[last_param_token] == .identifier and
+                token_tags[last_param_token + 1] == .colon)
+            {
                 try renderToken(ais, tree, last_param_token, .none); // name
                 last_param_token += 1;
                 try renderToken(ais, tree, last_param_token, .space); // :