diff --git a/tests/unit/test_fmha_v3_stage_c_full.py b/tests/unit/test_fmha_v3_stage_c_full.py
index 94b7a460..2dea592c 100644
--- a/tests/unit/test_fmha_v3_stage_c_full.py
+++ b/tests/unit/test_fmha_v3_stage_c_full.py
@@ -316,8 +316,10 @@ class FmhaV3StageC:
                     row_max_safe = Float32(0.0)
 
                 # acc_scale for both row_sum rescale and O rescale.
-                acc_scale_ = scale_log2 * (old_row_max - row_max_safe)
-                acc_scale = cute.math.exp2(acc_scale_, fastmath=True)
+                # row_max is already in log2(scaled) space (S * scale_log2),
+                # so the difference old_row_max - row_max_safe is already the
+                # correct exponent for exp2. No extra scale_log2 factor.
+                acc_scale = cute.math.exp2(old_row_max - row_max_safe, fastmath=True)
                 if old_row_max == -cutlass.Float32.inf:
                     acc_scale = Float32(0.0)
                 row_sum *= acc_scale