--- a/native/jni/java-math/gnu_java_math_GMP.c
+++ b/native/jni/java-math/gnu_java_math_GMP.c
@@ -1132,6 +1132,7 @@
         break;
       case 1:
         res = mpz_popcount (_this);
+      __attribute__((fallthrough));
       default:
         JCL_ThrowException (env, "java/lang/Error",
                             "Unexpected sign value for a native MPI");
