diff --git a/src-self-hosted/cbe.h b/src-self-hosted/cbe.h
index 691aa457252441de86ac23f8425a5c5ad3641164..854032227d1aed97b78f359c282efecb0f5f5e8b 100644
--- a/src-self-hosted/cbe.h
+++ b/src-self-hosted/cbe.h
@@ -8,3 +8,8 @@
 #define zig_noreturn
 #endif
 
+#if __GNUC__
+#define zig_unreachable() __builtin_unreachable()
+#else
+#define zig_unreachable()
+#endif
diff --git a/src-self-hosted/codegen/c.zig b/src-self-hosted/codegen/c.zig
index ba68a3a5a4fda833cfe1967d3e3f1d485c533f6c..591e47967e69a92c3cb99a3bb8dc4d79ac0e4711 100644
--- a/src-self-hosted/codegen/c.zig
+++ b/src-self-hosted/codegen/c.zig
@@ -178,7 +178,7 @@ fn genBreak(file: *C, inst: *Inst.NoOp, decl: *Decl) !void {
 }
 
 fn genUnreach(file: *C, inst: *Inst.NoOp, decl: *Decl) !void {
-    // TODO ??
+    try file.main.writer().writeAll("    zig_unreachable();\n");
 }
 
 fn genAsm(file: *C, as: *Inst.Assembly, decl: *Decl, argdex: *usize) !void {
diff --git a/test/stage2/cbe.zig b/test/stage2/cbe.zig
index 36c4514d49bab2042b477e550eb29857af2f22c5..59bc062b7450fc8fd01e8efb0ff28c651d42de14 100644
--- a/test/stage2/cbe.zig
+++ b/test/stage2/cbe.zig
@@ -65,7 +65,7 @@ pub fn addCases(ctx: *TestContext) !void {
         \\}
         \\
     );
-    ctx.c("exit", linux_x64,
+    ctx.c("exit with parameter", linux_x64,
         \\export fn _start() noreturn {
         \\    exit(0);
         \\}
@@ -96,6 +96,7 @@ pub fn addCases(ctx: *TestContext) !void {
         \\    register size_t rax_constant __asm__("rax") = 231;
         \\    register size_t rdi_constant __asm__("rdi") = arg0;
         \\    __asm volatile ("syscall" :: ""(rax_constant), ""(rdi_constant));
+        \\    zig_unreachable();
         \\}
         \\
     );