diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 212f01c..6eeb8fe 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -11,6 +11,7 @@ permissions:
 
 env:
   PYTHONIOENCODING: utf-8
+  PYTHONUTF8: "1"
 
 jobs:
   validate:
diff --git a/scripts/verify-drawio-import.py b/scripts/verify-drawio-import.py
index c8e0ecc..bb27586 100644
--- a/scripts/verify-drawio-import.py
+++ b/scripts/verify-drawio-import.py
@@ -48,6 +48,8 @@ def run_extract(args: list[str]) -> str:
         [sys.executable, str(EXTRACT), *args],
         capture_output=True,
         text=True,
+        encoding="utf-8",
+        errors="replace",
     )
     if proc.returncode != 0:
         fail(f"extractor exited {proc.returncode} for {args}: {proc.stderr.strip()}")
diff --git a/scripts/verify-mermaid-import.py b/scripts/verify-mermaid-import.py
index 78418e1..969bfa9 100644
--- a/scripts/verify-mermaid-import.py
+++ b/scripts/verify-mermaid-import.py
@@ -43,6 +43,8 @@ def invoke(args: list[str]) -> subprocess.CompletedProcess[str]:
         [sys.executable, str(EXTRACT), *args],
         capture_output=True,
         text=True,
+        encoding="utf-8",
+        errors="replace",
     )