diff --git a/src/protocols/vnc/vnc_handlers.c b/src/protocols/vnc/vnc_handlers.c
index 878e9a2e..020f2419 100644
--- a/src/protocols/vnc/vnc_handlers.c
+++ b/src/protocols/vnc/vnc_handlers.c
@@ -39,6 +39,7 @@
 #include <time.h>
 #include <syslog.h>
 #include <iconv.h>
+#include <pthread.h>
 
 #include <cairo/cairo.h>
 
@@ -132,12 +133,17 @@ void guac_vnc_cursor(rfbClient* client, int x, int y, int w, int h, int bpp) {
 
     /* Send cursor data*/
     surface = cairo_image_surface_create_for_data(buffer, CAIRO_FORMAT_ARGB32, w, h, stride);
+    
+    pthread_mutex_lock(&(gc->send_lock));
+    
     guac_protocol_send_png(socket,
             GUAC_COMP_SRC, cursor_layer, 0, 0, surface);
-
+    
+    pthread_mutex_unlock(&(gc->send_lock));
+    
     /* Update cursor */
     guac_protocol_send_cursor(socket, x, y, cursor_layer, 0, 0, w, h);
-
+    
     /* Free surface */
     cairo_surface_destroy(surface);
     free(buffer);
@@ -231,8 +237,13 @@ void guac_vnc_update(rfbClient* client, int x, int y, int w, int h) {
 
     /* For now, only use default layer */
     surface = cairo_image_surface_create_for_data(buffer, CAIRO_FORMAT_RGB24, w, h, stride);
+
+    pthread_mutex_lock(&(gc->send_lock));
+
     guac_protocol_send_png(socket, GUAC_COMP_OVER, GUAC_DEFAULT_LAYER, x, y, surface);
 
+    pthread_mutex_unlock(&(gc->send_lock));
+
     /* Free surface */
     cairo_surface_destroy(surface);
     free(buffer);
@@ -244,11 +255,15 @@ void guac_vnc_copyrect(rfbClient* client, int src_x, int src_y, int w, int h, in
     guac_client* gc = rfbClientGetClientData(client, __GUAC_CLIENT);
     guac_socket* socket = gc->socket;
 
+    pthread_mutex_lock(&(gc->send_lock));
+
     /* For now, only use default layer */
     guac_protocol_send_copy(socket,
                             GUAC_DEFAULT_LAYER, src_x,  src_y, w, h,
             GUAC_COMP_OVER, GUAC_DEFAULT_LAYER, dest_x, dest_y);
 
+    pthread_mutex_unlock(&(gc->send_lock));
+
     ((vnc_guac_client_data*) gc->data)->copy_rect_used = 1;
 
 }
@@ -301,10 +316,14 @@ rfbBool guac_vnc_malloc_framebuffer(rfbClient* rfb_client) {
     guac_client* gc = rfbClientGetClientData(rfb_client, __GUAC_CLIENT);
     vnc_guac_client_data* guac_client_data = (vnc_guac_client_data*) gc->data;
 
+    pthread_mutex_lock(&(gc->send_lock));
+
     /* Send new size */
     guac_protocol_send_size(gc->socket,
             GUAC_DEFAULT_LAYER, rfb_client->width, rfb_client->height);
 
+    pthread_mutex_unlock(&(gc->send_lock));
+
     /* Use original, wrapped proc */
     return guac_client_data->rfb_MallocFrameBuffer(rfb_client);
 }
@@ -317,8 +336,12 @@ void guac_vnc_cut_text(rfbClient* client, const char* text, int textlen) {
     /* Convert ASCII character data to UTF-8 */
     char* utf8_text = convert("ISO_8859-1", "UTF-8", text);
 
+    pthread_mutex_lock(&(gc->send_lock));
+
     guac_protocol_send_clipboard(socket, utf8_text);
 
+    pthread_mutex_unlock(&(gc->send_lock));
+
     free(utf8_text);
 
 }