diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5aad91f4..ed160f5c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1271,12 +1271,12 @@ calculation (with runtime detection) if supported by the compiler" ON)
                         && !defined(__EDG__)
                 __attribute__((__target__(\"ssse3,sse4.1,pclmul\")))
                 #endif
-                __m128i my_clmul(__m128i a)
+                int main(void)
                 {
-                    const __m128i b = _mm_set_epi64x(1, 2);
-                    return _mm_clmulepi64_si128(a, b, 0);
+                    __m128i a = _mm_set_epi64x(1, 2);
+                    a = _mm_clmulepi64_si128(a, a, 0);
+                    return 0;
                 }
-                int main(void) { return 0; }
             "
             HAVE_USABLE_CLMUL)
         tuklib_add_definition_if(liblzma HAVE_USABLE_CLMUL)
@@ -1301,11 +1301,10 @@ if(XZ_ARM64_CRC32)
             #if (defined(__GNUC__) || defined(__clang__)) && !defined(__EDG__)
             __attribute__((__target__(\"+crc\")))
             #endif
-            uint32_t my_crc(uint32_t a, uint64_t b)
+            int main(void)
             {
-                return __crc32d(a, b);
+                return __crc32d(1, 2) != 0;
             }
-            int main(void) { return 0; }
         "
         HAVE_ARM64_CRC32)
 
@@ -1773,16 +1772,14 @@ if(NOT SANDBOX_FOUND AND XZ_SANDBOX MATCHES "^auto$|^landlock$")
         #include <sys/syscall.h>
         #include <sys/prctl.h>
 
-        void my_sandbox(void)
+        int main(void)
         {
             (void)prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
             (void)SYS_landlock_create_ruleset;
             (void)SYS_landlock_restrict_self;
             (void)LANDLOCK_CREATE_RULESET_VERSION;
-            return;
+            return 0;
         }
-
-        int main(void) { return 0; }
         "
     HAVE_LINUX_LANDLOCK)