diff --git a/src/c_import.test.zig b/src/c_import.test.zig
index e889b89..2d53ff6 100644
--- a/src/c_import.test.zig
+++ b/src/c_import.test.zig
@@ -55,6 +55,15 @@ test "cSourceCacheKey: llvm version varies the key" {
     try std.testing.expect(baseKey() != other);
 }
 
+test "objectMagicOk: accepts Mach-O and ELF, rejects garbage and truncation" {
+    try std.testing.expect(c_import.objectMagicOk(&.{ 0xcf, 0xfa, 0xed, 0xfe, 0x00 })); // Mach-O 64
+    try std.testing.expect(c_import.objectMagicOk(&.{ 0xce, 0xfa, 0xed, 0xfe })); // Mach-O 32
+    try std.testing.expect(c_import.objectMagicOk(&.{ 0x7f, 'E', 'L', 'F', 0x02 }));
+    try std.testing.expect(!c_import.objectMagicOk("not an object file"));
+    try std.testing.expect(!c_import.objectMagicOk(&.{ 0xcf, 0xfa, 0xed })); // truncated magic
+    try std.testing.expect(!c_import.objectMagicOk(&.{}));
+}
+
 test "cSourceCacheKey: triple and sysroot vary the key; absent is not empty" {
     const other_triple = c_import.cSourceCacheKey(SRC, &.{HDR}, &.{"A=1"}, &.{"-O2"}, &.{"inc"}, VER, "x86_64-apple-darwin", "/sdk");
     try std.testing.expect(baseKey() != other_triple);