diff --git a/sapi/fpm/fpm/fpm_shm.c b/sapi/fpm/fpm/fpm_shm.c
index 386fef8c49fa2..7b27978084367 100644
--- a/sapi/fpm/fpm/fpm_shm.c
+++ b/sapi/fpm/fpm/fpm_shm.c
@@ -50,7 +50,7 @@ int fpm_shm_free(void *mem, size_t size) /* {{{ */
 		return 0;
 	}
 
-	if (fpm_shm_size - size > 0) {
+	if (fpm_shm_size > size) {
 		fpm_shm_size -= size;
 	} else {
 		fpm_shm_size = 0;