diff --git a/src/galloc.🗿 b/src/galloc.🗿
index f18e05d..6930136 100644
--- a/src/galloc.🗿
+++ b/src/galloc.🗿
@@ -144,6 +144,11 @@ free(ptr)
 	local first_block;
 	local last_block;
 
+	if (ptr > heap + HEAP_SIZE | heap > ptr)
+	{
+		putstr("Error: free: invalid ptr\n");
+		return;
+	}
 	block = ptr - LOCATION_DATA;
 	prev_block = [block + LOCATION_PREV];
 	if (prev_block == 0 | [prev_block + LOCATION_USED])
@@ -160,5 +165,5 @@ free(ptr)
 
 leaks()
 {
-	return (heap + LOCATION_NEXT != NULL);
+	return ([heap + LOCATION_NEXT] != 0);
 }
diff --git a/tests/galloc.🗿 b/tests/galloc.🗿
index c55e6b9..5a05516 100644
--- a/tests/galloc.🗿
+++ b/tests/galloc.🗿
@@ -16,7 +16,9 @@ main()
 
 	ptr2 = galloc(0x9000);
 	test_num(ptr2, 0, "alloc too big");
-	free(ptr2);
 
+	test_num(leaks(), 0, "leaks");
+	ptr1 = galloc(1);
 	test_num(leaks(), 1, "leaks");
+	free(ptr1);
 }