diff --git a/tools/hw-oracle/hw_oracle.py b/tools/hw-oracle/hw_oracle.py
index 6cb1c4738..fbecb317e 100644
--- a/tools/hw-oracle/hw_oracle.py
+++ b/tools/hw-oracle/hw_oracle.py
@@ -89,8 +89,9 @@ def run(body, rows, extra=b"", wave64=False, coarse=False, *, ieee, denorm32, de
         work = Path(tmp)
         code = assemble(body, work, wave64, ieee=ieee, denorm32=denorm32, denorm16=denorm16,
                         dx10_clamp=dx10_clamp, round32=round32, round16=round16, fp16_overflow=fp16_overflow, lds=lds)
-        for start in range(0, len(padded), ROWS_PER_DISPATCH):
-            chunk = padded[start:start + ROWS_PER_DISPATCH]
+        rows_per_dispatch = ROWS_PER_DISPATCH // 2 if wave64 else ROWS_PER_DISPATCH
+        for start in range(0, len(padded), rows_per_dispatch):
+            chunk = padded[start:start + rows_per_dispatch]
             (work / "in.bin").write_bytes(b"".join(struct.pack("<4I", *r) for r in chunk) + extra)
             subprocess.run([oracle(), str(code), str(len(chunk)), str(work / "in.bin"), str(work / "out.bin"), "16"], check=True, env=env)
             data = (work / "out.bin").read_bytes()
diff --git a/tools/hw-oracle/test_hw_oracle.py b/tools/hw-oracle/test_hw_oracle.py
index 0b8ad0ea9..606517706 100644
--- a/tools/hw-oracle/test_hw_oracle.py
+++ b/tools/hw-oracle/test_hw_oracle.py
@@ -123,6 +123,25 @@ class FloatModeTests(unittest.TestCase):
 
 
 class GroupSegmentTests(unittest.TestCase):
+    def test_wave64_dispatches_at_most_512_rows(self):
+        rows = [(index, 0, 0, 0) for index in range(1025)]
+        for wave64, expected in ((False, [1024, 32]), (True, [512, 512, 64])):
+            with self.subTest(wave64=wave64), tempfile.TemporaryDirectory() as tmp:
+                dispatch_sizes = []
+
+                def dispatch(command, *, check, env):
+                    self.assertTrue(check)
+                    dispatch_sizes.append(int(command[2]))
+                    Path(command[4]).write_bytes(bytes(int(command[2]) * 64))
+
+                with patch.object(hw_oracle, "assemble", return_value=Path(tmp) / "kernel.co"), \
+                        patch.object(hw_oracle, "oracle", return_value="oracle"), \
+                        patch.object(hw_oracle.subprocess, "run", side_effect=dispatch):
+                    result = hw_oracle.run("s_nop 0", rows, wave64=wave64, **MODES)
+
+                self.assertEqual(dispatch_sizes, expected)
+                self.assertEqual(len(result), len(rows))
+
     def test_cli_forwards_lds(self):
         with tempfile.TemporaryDirectory() as tmp:
             body = Path(tmp) / "body.s"