diff --git a/tools/build/compile_shader_spirv.py b/tools/build/compile_shader_spirv.py
index 2f7eb262c..49dec0786 100644
--- a/tools/build/compile_shader_spirv.py
+++ b/tools/build/compile_shader_spirv.py
@@ -107,7 +107,7 @@ def main():
         if result.returncode != 0:
             print(f"ERROR: glslangValidator failed for {src_name}", file=sys.stderr)
             if result.stderr:
-                sys.stderr.write(result.stderr)
+                sys.stderr.buffer.write(result.stderr)
             return 1
 
         # Step 2: spirv-opt
@@ -118,7 +118,7 @@ def main():
         if result.returncode != 0:
             print(f"ERROR: spirv-opt failed for {src_name}", file=sys.stderr)
             if result.stderr:
-                sys.stderr.write(result.stderr)
+                sys.stderr.buffer.write(result.stderr)
             return 1
 
         # Step 3: spirv-dis
@@ -127,7 +127,7 @@ def main():
         if result.returncode != 0:
             print(f"ERROR: spirv-dis failed for {src_name}", file=sys.stderr)
             if result.stderr:
-                sys.stderr.write(result.stderr)
+                sys.stderr.buffer.write(result.stderr)
             return 1
 
         # Step 4: Generate header