diff --git a/openbsc/contrib/nat/test_regexp.c b/openbsc/contrib/nat/test_regexp.c
new file mode 100644
index 000000000..808a703ca
--- /dev/null
+++ b/openbsc/contrib/nat/test_regexp.c
@@ -0,0 +1,30 @@
+/* make test_regexp */
+#include <sys/types.h>
+#include <regex.h>
+#include <stdio.h>
+
+
+int main(int argc, char **argv)
+{
+	regex_t reg;
+	regmatch_t matches[2];
+
+	if (argc != 4) {
+		printf("Invoke with: test_regexp REGEXP REPLACE NR\n");
+		return -1;
+	}
+
+	if (regcomp(&reg, argv[1], REG_EXTENDED) != 0) {
+		fprintf(stderr, "Regexp '%s' is not valid.\n", argv[1]);
+		return -1;
+	}
+
+	if (regexec(&reg, argv[3], 2, matches, 0) == 0 && matches[1].rm_eo != -1)
+		printf("New Number: %s%s\n", argv[2], &argv[3][matches[1].rm_so]);
+	else
+		printf("No match.\n");
+
+	regfree(&reg);
+
+	return 0;
+}