diff --git a/res/res_features.c b/res/res_features.c
index e4d3645f31..bc045bb9df 100644
--- a/res/res_features.c
+++ b/res/res_features.c
@@ -305,6 +305,23 @@ static int metermaidstate(const char *data)
 		return AST_DEVICE_INUSE;
 }
 
+/*!
+ * \brief Check to see if a parking space is in use
+ * \return non-zero if in use, zero if not in use
+ * \note Assumes parking_lock is locked
+ */
+static int check_parking_space_inuse(int space)
+{
+	struct parkeduser *pu;
+
+	for (pu = parkinglot; pu; pu = pu->next) {
+		if (pu->parkingnum == space)
+			return 1;
+	}
+
+	return 0;
+}
+
 /*! \brief Park a call 
  	\note We put the user in the parking list, then wake up the parking thread to be sure it looks
 	after these channels too */
@@ -330,6 +347,12 @@ int ast_park_call(struct ast_channel *chan, struct ast_channel *peer, int timeou
 		}
 		ast_copy_string(pu->parkingexten, parkingexten, sizeof(pu->parkingexten));
 		x = atoi(parkingexten);
+		if (check_parking_space_inuse(x)) {
+			ast_mutex_unlock(&parking_lock);
+			free(pu);
+			ast_log(LOG_WARNING, "Requested parking space %d via PARKINGEXTEN, but it is in use!\n", x);
+			return -1;
+		}
 	} else {
 		/* Select parking space within range */
 		parking_range = parking_stop - parking_start+1;