diff --git a/debian/dump1090-mutability.config b/debian/dump1090-mutability.config
index a55d2cc..871c483 100644
--- a/debian/dump1090-mutability.config
+++ b/debian/dump1090-mutability.config
@@ -133,7 +133,7 @@ is_ipaddrish_or_empty() {
 }
 
 is_number() {
-  if echo "$1" | grep -Eq '^(0|[+-]?[1-9][0-9]*)(\.[0-9]+)?$'; then return 0; else return 1; fi
+  if echo "$1" | grep -Eq '^([+-]?[0-9][0-9]*)(\.[0-9]+)?$'; then return 0; else return 1; fi
 }
 
 is_number_or_empty() {