diff --git a/test/stage1/behavior.zig b/test/stage1/behavior.zig
index 525d65d7fc..f7fc1c42a4 100644
--- a/test/stage1/behavior.zig
+++ b/test/stage1/behavior.zig
@@ -20,6 +20,7 @@ comptime {
     _ = @import("behavior/bugs/1486.zig");
     _ = @import("behavior/bugs/1851.zig");
     _ = @import("behavior/bugs/394.zig");
+    _ = @import("behavior/bugs/421.zig");
     _ = @import("behavior/bugs/655.zig");
     _ = @import("behavior/bugs/656.zig");
     _ = @import("behavior/bugs/726.zig");
diff --git a/test/stage1/behavior/bugs/421.zig b/test/stage1/behavior/bugs/421.zig
new file mode 100644
index 0000000000..e5f67f61b7
--- /dev/null
+++ b/test/stage1/behavior/bugs/421.zig
@@ -0,0 +1,16 @@
+const assert = @import("std").debug.assert;
+
+test "bitCast to array" {
+    comptime testBitCastArray();
+    testBitCastArray();
+}
+
+fn testBitCastArray() void {
+    assert(extractOne64(0x0123456789abcdef0123456789abcdef) == 0x0123456789abcdef);
+}
+
+fn extractOne64(a: u128) u64 {
+    const x = @bitCast([2]u64, a);
+    return x[1];
+}
+