diff --git a/src/ngscopeclient/shaders/waveform-compute.glsl b/src/ngscopeclient/shaders/waveform-compute.glsl
index 049c645e..e7979839 100644
--- a/src/ngscopeclient/shaders/waveform-compute.glsl
+++ b/src/ngscopeclient/shaders/waveform-compute.glsl
@@ -236,21 +236,26 @@ void main()
        }

        //Setup for main loop
+       bool l_done = false;
+
        if(gl_LocalInvocationID.y == 0)
                g_done = false;

+       barrier();
+       memoryBarrierShared();
+
        #ifdef DENSE_PACK
                uint istart = uint(floor(gl_GlobalInvocationID.x / xscale)) + offset_samples;
                uint iend = uint(floor((gl_GlobalInvocationID.x + 1) / xscale)) + offset_samples;
                if(iend <= 0)
-                       g_done = true;
+                       l_done = true;
        #else
                uint istart = xind[gl_GlobalInvocationID.x];
                if( (gl_GlobalInvocationID.x + 1) < windowWidth)
                {
                        uint iend = xind[gl_GlobalInvocationID.x + 1];
                        if(iend <= 0)
-                               g_done = true;
+                               l_done = true;
                }
        #endif
        uint i = istart + gl_GlobalInvocationID.y;
@@ -369,17 +374,20 @@ void main()

                        //Check if we're at the end of the pixel
                        if(right.x > gl_GlobalInvocationID.x + 1)
-                               g_done = true;
+                               l_done = true;
                }

                else
                {
-                       g_done = true;
+                       l_done = true;
                        g_updating[gl_LocalInvocationID.y] = false;
                }

                i += ROWS_PER_BLOCK;

+               if (l_done)
+                       g_done = true;
+
                //Only update if we need to
                for(int y = 0; y<ROWS_PER_BLOCK; y++)
                {