diff --git a/src/guest/maple/controller.c b/src/guest/maple/controller.c
index b0eaa158..306dfdab 100644
--- a/src/guest/maple/controller.c
+++ b/src/guest/maple/controller.c
@@ -34,9 +34,9 @@ struct controller {
   struct maple_cond cnd;
 };
 
-static void controller_frame(struct maple_device *dev,
-                             const union maple_frame *req,
-                             union maple_frame *res) {
+static int controller_frame(struct maple_device *dev,
+                            const union maple_frame *req,
+                            union maple_frame *res) {
   struct controller *ctrl = (struct controller *)dev;
 
   /* forward to sub-device if specified */
@@ -45,8 +45,7 @@ static void controller_frame(struct maple_device *dev,
 
   struct maple_device *sub = maple_get_device(dev->mp, port, unit);
   if (sub != dev) {
-    sub->frame(sub, req, res);
-    return;
+    return sub && sub->frame(sub, req, res);
   }
 
   switch (req->command) {
@@ -98,6 +97,8 @@ static void controller_frame(struct maple_device *dev,
 
     res->src_addr |= 1 << i;
   }
+
+  return 1;
 }
 
 static int controller_input(struct maple_device *dev, int button,
diff --git a/src/guest/maple/maple.c b/src/guest/maple/maple.c
index bda9a4c8..522c74bf 100644
--- a/src/guest/maple/maple.c
+++ b/src/guest/maple/maple.c
@@ -49,12 +49,7 @@ int maple_handle_frame(struct maple *mp, int port, union maple_frame *frame,
      frame data bswap'd. for this reason, it's not valid to inspect the frame
      data in order to send the frame directly to the correct sub-device */
   struct maple_device *dev = mp->devs[port][MAPLE_MAX_UNITS - 1];
-  if (!dev) {
-    return 0;
-  }
-
-  dev->frame(dev, frame, res);
-  return 1;
+  return dev && dev->frame(dev, frame, res);
 }
 
 void maple_handle_input(struct maple *mp, int port, int button,
diff --git a/src/guest/maple/maple.h b/src/guest/maple/maple.h
index 1b7d090d..75f6d38f 100644
--- a/src/guest/maple/maple.h
+++ b/src/guest/maple/maple.h
@@ -11,8 +11,8 @@ struct maple_device {
   struct maple *mp;
   void (*destroy)(struct maple_device *);
   int (*input)(struct maple_device *, int, uint16_t);
-  void (*frame)(struct maple_device *, const union maple_frame *,
-                union maple_frame *);
+  int (*frame)(struct maple_device *, const union maple_frame *,
+               union maple_frame *);
 };
 
 uint8_t maple_encode_addr(int port, int unit);
diff --git a/src/guest/maple/vmu.c b/src/guest/maple/vmu.c
index 90764cf2..87714a81 100644
--- a/src/guest/maple/vmu.c
+++ b/src/guest/maple/vmu.c
@@ -53,8 +53,8 @@ static void vmu_parse_block_param(uint32_t data, int *partition, int *block,
   *phase = (data >> 8) & 0xff;
 }
 
-static void vmu_frame(struct maple_device *dev, const union maple_frame *req,
-                      union maple_frame *res) {
+static int vmu_frame(struct maple_device *dev, const union maple_frame *req,
+                     union maple_frame *res) {
   struct vmu *vmu = (struct vmu *)dev;
 
   switch (req->command) {
@@ -155,6 +155,8 @@ static void vmu_frame(struct maple_device *dev, const union maple_frame *req,
       res->num_words = 0;
     } break;
   }
+
+  return 1;
 }
 
 static void vmu_destroy(struct maple_device *dev) {