diff --git a/tests/unit/test_umma_qk.cu b/tests/unit/test_umma_qk.cu
index 556beb0e..903243d7 100644
--- a/tests/unit/test_umma_qk.cu
+++ b/tests/unit/test_umma_qk.cu
@@ -71,9 +71,10 @@ test_umma_qk_hd16(
     __syncthreads();
     uint32_t tmem_base = *sTmemBase;
 
-    // Zero TMEM
+    // Zero TMEM — test: only zero first 32 columns (min power of 2)
+    // Note: 128 columns might be too many for tmem_store in a loop
     if (wid == 0) {
-        for (int col = 0; col < 128; col++) {
+        for (int col = 0; col < 32; col++) {
             tmem_store(tmem_base + col, 0, 0, 0, 0);
         }
         tmem_fence_store();