diff --git a/kernel/heavyhash.cl b/kernel/heavyhash.cl
index d7d83ae..64326a3 100644
--- a/kernel/heavyhash.cl
+++ b/kernel/heavyhash.cl
@@ -78,6 +78,9 @@ __kernel void search(__global uint *header, __global uint* gmatrix, __global uin
 
     for (int i = 0; i < 64; ++i) {
         uint sum = 0;
+#ifdef __gfx900__
+        #pragma nounroll
+#endif
         for (int k = 0; k < 4; k++) {
             ulong2 buf0 = matrix[i * 16 + k * 4 + 0];
             ulong2 buf1 = matrix[i * 16 + k * 4 + 1];