diff --git a/src/config.c b/src/config.c
index 20f09d9..8ddfe26 100644
--- a/src/config.c
+++ b/src/config.c
@@ -355,6 +355,8 @@ load_config( const char *where, int pseudo )
 				if (store) {
 					if (!store->max_size)
 						store->max_size = INT_MAX;
+					if (!store->flat_delim)
+						store->flat_delim = "";
 					*storeapp = store;
 					storeapp = &store->next;
 					*storeapp = 0;
diff --git a/src/main.c b/src/main.c
index 3ba4323..eadd81f 100644
--- a/src/main.c
+++ b/src/main.c
@@ -983,7 +983,7 @@ store_connected( int sts, void *aux )
 							flags |= LIST_INBOX;
 						} else if (c == '/') {
 							/* Flattened sub-folders of INBOX actually end up in Path. */
-							if (mvars->ctx[t]->conf->flat_delim)
+							if (mvars->ctx[t]->conf->flat_delim[0])
 								flags |= LIST_PATH;
 							else
 								flags |= LIST_INBOX;
@@ -1027,7 +1027,7 @@ store_listed( int sts, string_list_t *boxes, void *aux )
 		return;
 	case DRV_OK:
 		for (box = boxes; box; box = box->next) {
-			if (mvars->ctx[t]->conf->flat_delim) {
+			if (mvars->ctx[t]->conf->flat_delim[0]) {
 				string_list_t *nbox;
 				if (map_name( box->string, (char **)&nbox, offsetof(string_list_t, string), mvars->ctx[t]->conf->flat_delim, "/" ) < 0) {
 					error( "Error: flattened mailbox name '%s' contains canonical hierarchy delimiter\n", box->string );
diff --git a/src/sync.c b/src/sync.c
index 8f2b4a2..7397db2 100644
--- a/src/sync.c
+++ b/src/sync.c
@@ -1014,7 +1014,7 @@ sync_boxes( store_t *ctx[], const char *names[], int present[], channel_conf_t *
 		svars->orig_name[t] =
 			(!names[t] || (ctx[t]->conf->map_inbox && !strcmp( ctx[t]->conf->map_inbox, names[t] ))) ?
 				"INBOX" : names[t];
-		if (!ctx[t]->conf->flat_delim) {
+		if (!ctx[t]->conf->flat_delim[0]) {
 			svars->box_name[t] = nfstrdup( svars->orig_name[t] );
 		} else if (map_name( svars->orig_name[t], &svars->box_name[t], 0, "/", ctx[t]->conf->flat_delim ) < 0) {
 			error( "Error: canonical mailbox name '%s' contains flattened hierarchy delimiter\n", svars->orig_name[t] );
diff --git a/src/util.c b/src/util.c
index 3b624bd..f4dce49 100644
--- a/src/util.c
+++ b/src/util.c
@@ -479,19 +479,20 @@ map_name( const char *arg, char **result, int reserve, const char *in, const cha
 	char *p;
 	int i, l, ll, num, inl, outl;
 
+	assert( arg );
 	l = strlen( arg );
-	if (!in) {
+	assert( in );
+	inl = strlen( in );
+	if (!inl) {
 	  copy:
 		*result = nfmalloc( reserve + l + 1 );
 		memcpy( *result + reserve, arg, l + 1 );
 		return 0;
 	}
-	inl = strlen( in );
-	if (out) {
-		outl = strlen( out );
-		if (inl == outl && !memcmp( in, out, inl ))
-			goto copy;
-	}
+	assert( out );
+	outl = strlen( out );
+	if (inl == outl && !memcmp( in, out, inl ))
+		goto copy;
 	for (num = 0, i = 0; i < l; ) {
 		for (ll = 0; ll < inl; ll++)
 			if (arg[i + ll] != in[ll])
@@ -500,7 +501,7 @@ map_name( const char *arg, char **result, int reserve, const char *in, const cha
 		i += inl;
 		continue;
 	  fout:
-		if (out) {
+		if (outl) {
 			for (ll = 0; ll < outl; ll++)
 				if (arg[i + ll] != out[ll])
 					goto fnexti;
@@ -511,7 +512,7 @@ map_name( const char *arg, char **result, int reserve, const char *in, const cha
 	}
 	if (!num)
 		goto copy;
-	if (!out)
+	if (!outl)
 		return -2;
 	*result = nfmalloc( reserve + l + num * (outl - inl) + 1 );
 	p = *result + reserve;
@@ -519,15 +520,7 @@ map_name( const char *arg, char **result, int reserve, const char *in, const cha
 		for (ll = 0; ll < inl; ll++)
 			if (arg[i + ll] != in[ll])
 				goto rnexti;
-#if defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)) && !defined(__clang__)
-# pragma GCC diagnostic push
-/* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42145 */
-# pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
-#endif
 		memcpy( p, out, outl );
-#if defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)) && !defined(__clang__)
-# pragma GCC diagnostic pop
-#endif
 		p += outl;
 		i += inl;
 		continue;