diff --git a/channels/chan_dahdi.c b/channels/chan_dahdi.c
index d68876a7f0..cdfb867b39 100644
--- a/channels/chan_dahdi.c
+++ b/channels/chan_dahdi.c
@@ -5679,7 +5679,10 @@ static struct ast_frame  *dahdi_read(struct ast_channel *ast)
 		return NULL;
 	}
 	
-	if ((p->radio || (p->oprmode < 0)) && p->inalarm) return NULL;
+	if ((p->radio || (p->oprmode < 0)) && p->inalarm) {
+		ast_mutex_unlock(&p->lock);
+		return NULL;
+	}
 
 	p->subs[idx].f.frametype = AST_FRAME_NULL;
 	p->subs[idx].f.datalen = 0;