diff --git a/third_party/amd/backend/driver.py b/third_party/amd/backend/driver.py
index b10def16bc..99e5509eca 100644
--- a/third_party/amd/backend/driver.py
+++ b/third_party/amd/backend/driver.py
@@ -220,7 +220,7 @@ def format_of(ty):
             "int8_t": "b",
             "int16_t": "h",
             "int32_t": "i",
-            "int64_t": "l",
+            "int64_t": "L",
             "uint8_t": "B",
             "uint16_t": "H",
             "uint32_t": "I",
diff --git a/third_party/nvidia/backend/driver.py b/third_party/nvidia/backend/driver.py
index 1114cebe33..196f189caa 100644
--- a/third_party/nvidia/backend/driver.py
+++ b/third_party/nvidia/backend/driver.py
@@ -139,7 +139,7 @@ def format_of(ty):
             "int8_t": "b",
             "int16_t": "h",
             "int32_t": "i",
-            "int64_t": "l",
+            "int64_t": "L",
             "uint8_t": "B",
             "uint16_t": "H",
             "uint32_t": "I",