diff --git a/openbsc/src/nat/bsc_nat_utils.c b/openbsc/src/nat/bsc_nat_utils.c
index aba082d..b43d67a 100644
--- a/openbsc/src/nat/bsc_nat_utils.c
+++ b/openbsc/src/nat/bsc_nat_utils.c
@@ -819,6 +819,12 @@
 		return msg;
 	}
 
+	if (strlen(new_number) > sizeof(called.number)) {
+		LOGP(DNAT, LOGL_ERROR, "Number is too long for structure.\n");
+		talloc_free(new_number);
+		return msg;
+	}
+
 	/*
 	 * Need to create a new message now based on the old onew
 	 * with a new number. We can sadly not patch this in place