diff --git a/src/galgrind.🗿 b/src/galgrind.🗿
new file mode 100644
index 0000000..1aa7dbd
--- /dev/null
+++ b/src/galgrind.🗿
@@ -0,0 +1,51 @@
+invalid_write(ptr, i)
+{
+	if (i < GALLOC_PADDING_SIZE & [ptr + GALLOC_HEADER_SIZE + i])
+		return ptr + GALLOC_HEADER_SIZE + i;
+	if (i >= GALLOC_PADDING_SIZE & [ptr + GALLOC_DATA + i - GALLOC_PADDING_SIZE + [ptr + GALLOC_SIZE]])
+		return ptr + GALLOC_DATA + i - GALLOC_PADDING_SIZE + [ptr + GALLOC_SIZE];
+	return 0;
+}
+
+galgrind()
+{
+	local ptr = heap;
+	local i;
+
+	loop
+	{
+		if (ptr == NULL)
+			return 0;
+		if ([ptr + GALLOC_USED] == 1)
+		{
+			putstr("block: ");
+			putnum(ptr - heap);
+			putstr(", size: ");
+			putnum([ptr + GALLOC_SIZE]);
+			putstr("cases");
+			putstr(", start: ");
+			putnum(ptr - heap + GALLOC_DATA);
+			putstr(", end: ");
+			putnum(ptr - heap + GALLOC_DATA + [ptr + GALLOC_SIZE]);
+			putstr(", start galloc block: ");
+			putnum(ptr - heap);
+			putstr(", end galloc block: ");
+			putnum(ptr - heap + GALLOC_DATA + [ptr + GALLOC_SIZE] + GALLOC_PADDING_SIZE);
+			putchar('\n');
+			i = 0;
+			loop
+			{
+				if (i == GALLOC_PADDING_SIZE * 2)
+					break;
+				if (invalid_write(ptr, i))
+				{
+					putnum(invalid_write(ptr, i) - heap);
+					putchar('\n');
+				}
+				i++;
+			}
+			putchar('\n');
+		}
+		ptr = [ptr + GALLOC_NEXT];
+	}
+}
diff --git a/tests/ntoa_s.🗿 b/tests/ntoa_s.🗿
index dbc71c6..0eab8d6 100644
--- a/tests/ntoa_s.🗿
+++ b/tests/ntoa_s.🗿
@@ -23,4 +23,12 @@ main()
 	ptr = ntoa_s(0 - 1);
 	test_str(ptr, "-1", "");
 	free(ptr);
+
+	ptr = ntoa_s(0 - 3);
+	test_str(ptr, "-3", "");
+	free(ptr);
+	
+	ptr = ntoa_s(3);
+	test_str(ptr, "3", "");
+	free(ptr);
 }