diff --git a/tests/ctypesgentest.py b/tests/ctypesgentest.py
index e44eee3a..d927b00a 100644
--- a/tests/ctypesgentest.py
+++ b/tests/ctypesgentest.py
@@ -35,7 +35,7 @@ def generate(header_str, args=[], lang="py"):
     tmp_header = tempfile.NamedTemporaryFile()
     tmp_header.write(header_str.encode())
     tmp_header.seek(0)
-    tmp_out = tempfile.NamedTemporaryFile()
+    tmp_out = tempfile.NamedTemporaryFile(mode="w")
     ctypesgen_main(["-i", tmp_header.name, "-o", tmp_out.name, "--output-language", lang, *args])
     
     tmp_header_name = tmp_header.name
diff --git a/tests/testsuite.py b/tests/testsuite.py
index b1d3309d..a82a7c17 100755
--- a/tests/testsuite.py
+++ b/tests/testsuite.py
@@ -2550,7 +2550,7 @@ class MacromanEncodeTest(unittest.TestCase):
 
     @classmethod
     def setUpClass(cls):
-        cls.mac_roman_file = "temp_mac.h"
+        cls.mac_roman_file = TEST_DIR/"temp_mac.h"
         mac_header_str = b"""
         #define kICHelper                       "\xa9\\pHelper\xa5"
 
@@ -2559,8 +2559,8 @@ def setUpClass(cls):
         with open(cls.mac_roman_file, "wb") as mac_file:
             mac_file.write(mac_header_str)
 
-        header_str = """
-        #include "temp_mac.h"
+        header_str = f"""
+        #include "{cls.mac_roman_file}"
 
         #define MYSTRING kICHelper