diff --git a/ui/cocoa.m b/ui/cocoa.m
index e2567d6946..2931c751fd 100644
--- a/ui/cocoa.m
+++ b/ui/cocoa.m
@@ -129,6 +129,21 @@
 NSTextField *pauseLabel;
 NSArray * supportedImageFileTypes;
 
+// Utility function to run specified code block with iothread lock held
+typedef void (^CodeBlock)(void);
+
+static void with_iothread_lock(CodeBlock block)
+{
+    bool locked = qemu_mutex_iothread_locked();
+    if (!locked) {
+        qemu_mutex_lock_iothread();
+    }
+    block();
+    if (!locked) {
+        qemu_mutex_unlock_iothread();
+    }
+}
+
 // Mac to QKeyCode conversion
 const int mac_to_qkeycode_map[] = {
     [kVK_ANSI_A] = Q_KEY_CODE_A,
@@ -306,6 +321,7 @@ - (void) ungrabMouse;
 - (void) toggleFullScreen:(id)sender;
 - (void) handleMonitorInput:(NSEvent *)event;
 - (void) handleEvent:(NSEvent *)event;
+- (void) handleEventLocked:(NSEvent *)event;
 - (void) setAbsoluteEnabled:(BOOL)tIsAbsoluteEnabled;
 /* The state surrounding mouse grabbing is potentially confusing.
  * isAbsoluteEnabled tracks qemu_input_is_absolute() [ie "is the emulated
@@ -649,8 +665,14 @@ - (void) handleMonitorInput:(NSEvent *)event
 
 - (void) handleEvent:(NSEvent *)event
 {
-    COCOA_DEBUG("QemuCocoaView: handleEvent\n");
+    with_iothread_lock(^{
+        [self handleEventLocked:event];
+    });
+}
 
+- (void) handleEventLocked:(NSEvent *)event
+{
+    COCOA_DEBUG("QemuCocoaView: handleEvent\n");
     int buttons = 0;
     int keycode = 0;
     bool mouse_event = false;
@@ -945,15 +967,18 @@ - (QEMUScreen) gscreen {return screen;}
  */
 - (void) raiseAllKeys
 {
-    int index;
     const int max_index = ARRAY_SIZE(modifiers_state);
 
-   for (index = 0; index < max_index; index++) {
-       if (modifiers_state[index]) {
-           modifiers_state[index] = 0;
-           qemu_input_event_send_key_qcode(dcl->con, index, false);
-       }
-   }
+    with_iothread_lock(^{
+        int index;
+
+        for (index = 0; index < max_index; index++) {
+            if (modifiers_state[index]) {
+                modifiers_state[index] = 0;
+                qemu_input_event_send_key_qcode(dcl->con, index, false);
+            }
+        }
+    });
 }
 @end
 
@@ -1215,13 +1240,17 @@ - (void)removePause
 /* Restarts QEMU */
 - (void)restartQEMU:(id)sender
 {
-    qmp_system_reset(NULL);
+    with_iothread_lock(^{
+        qmp_system_reset(NULL);
+    });
 }
 
 /* Powers down QEMU */
 - (void)powerDownQEMU:(id)sender
 {
-    qmp_system_powerdown(NULL);
+    with_iothread_lock(^{
+        qmp_system_powerdown(NULL);
+    });
 }
 
 /* Ejects the media.
@@ -1237,9 +1266,11 @@ - (void)ejectDeviceMedia:(id)sender
         return;
     }
 
-    Error *err = NULL;
-    qmp_eject(true, [drive cStringUsingEncoding: NSASCIIStringEncoding],
-              false, NULL, false, false, &err);
+    __block Error *err = NULL;
+    with_iothread_lock(^{
+        qmp_eject(true, [drive cStringUsingEncoding: NSASCIIStringEncoding],
+                  false, NULL, false, false, &err);
+    });
     handleAnyDeviceErrors(err);
 }
 
@@ -1271,16 +1302,18 @@ - (void)changeDeviceMedia:(id)sender
             return;
         }
 
-        Error *err = NULL;
-        qmp_blockdev_change_medium(true,
-                                   [drive cStringUsingEncoding:
-                                          NSASCIIStringEncoding],
-                                   false, NULL,
-                                   [file cStringUsingEncoding:
-                                         NSASCIIStringEncoding],
-                                   true, "raw",
-                                   false, 0,
-                                   &err);
+        __block Error *err = NULL;
+        with_iothread_lock(^{
+            qmp_blockdev_change_medium(true,
+                                       [drive cStringUsingEncoding:
+                                                  NSASCIIStringEncoding],
+                                       false, NULL,
+                                       [file cStringUsingEncoding:
+                                                 NSASCIIStringEncoding],
+                                       true, "raw",
+                                       false, 0,
+                                       &err);
+        });
         handleAnyDeviceErrors(err);
     }
 }
@@ -1419,7 +1452,9 @@ - (void)adjustSpeed:(id)sender
     // get the throttle percentage
     throttle_pct = [sender tag];
 
-    cpu_throttle_set(throttle_pct);
+    with_iothread_lock(^{
+        cpu_throttle_set(throttle_pct);
+    });
     COCOA_DEBUG("cpu throttling at %d%c\n", cpu_throttle_get_percentage(), '%');
 }
 
