diff --git a/src/smsutil.c b/src/smsutil.c
index e41c0416..8d620f2b 100644
--- a/src/smsutil.c
+++ b/src/smsutil.c
@@ -2314,7 +2314,7 @@ static void sms_assembly_load(struct sms_assembly *assembly,
 				const struct dirent *dir)
 {
 	struct sms_address addr;
-	char straddr[25];
+	DECLARE_SMS_ADDR_STR(straddr);
 	guint16 ref;
 	guint8 max;
 	guint8 seq;
@@ -2391,7 +2391,7 @@ static gboolean sms_assembly_store(struct sms_assembly *assembly,
 {
 	unsigned char buf[177];
 	int len;
-	char straddr[25];
+	DECLARE_SMS_ADDR_STR(straddr);
 
 	if (!assembly->imsi)
 		return FALSE;
diff --git a/src/smsutil.h b/src/smsutil.h
index 66ef6f8d..630fde48 100644
--- a/src/smsutil.h
+++ b/src/smsutil.h
@@ -432,6 +432,12 @@ gboolean sms_decode_unpacked_stk_pdu(const unsigned char *pdu, int len,
 gboolean sms_encode(const struct sms *in, int *len, int *tpdu_len,
 			unsigned char *pdu);
 
+/*
+ * Length is based on the address being 12 hex characters plus a
+ * terminating NUL char. See sms_assembly_extract_address().
+ */
+#define DECLARE_SMS_ADDR_STR(a) char a[25]
+
 gboolean sms_decode_address_field(const unsigned char *pdu, int len,
 					int *offset, gboolean sc,
 					struct sms_address *out);