diff --git a/src/tools.c b/src/tools.c
index 590a101..27e603a 100644
--- a/src/tools.c
+++ b/src/tools.c
@@ -2304,6 +2304,9 @@
 const char *parse_size_err(const char *text, unsigned *ret) {
 	unsigned value = 0;
 
+	if (!isdigit((unsigned char)*text))
+		return text;
+
 	while (1) {
 		unsigned int j;