diff --git a/parallel_orchestrator.py b/parallel_orchestrator.py
index 574cbd2c..e04e54f8 100644
--- a/parallel_orchestrator.py
+++ b/parallel_orchestrator.py
@@ -511,11 +511,14 @@ def _spawn_coding_agent(self, feature_id: int) -> tuple[bool, str]:
         try:
             # CREATE_NO_WINDOW on Windows prevents console window pop-ups
             # stdin=DEVNULL prevents blocking on stdin reads
+            # encoding="utf-8" and errors="replace" fix Windows CP1252 issues (#138)
             popen_kwargs = {
                 "stdin": subprocess.DEVNULL,
                 "stdout": subprocess.PIPE,
                 "stderr": subprocess.STDOUT,
                 "text": True,
+                "encoding": "utf-8",
+                "errors": "replace",
                 "cwd": str(AUTOCODER_ROOT),  # Run from autocoder root for proper imports
                 "env": {**os.environ, "PYTHONUNBUFFERED": "1"},
             }
@@ -600,11 +603,14 @@ def _spawn_testing_agent(self) -> tuple[bool, str]:
             try:
                 # CREATE_NO_WINDOW on Windows prevents console window pop-ups
                 # stdin=DEVNULL prevents blocking on stdin reads
+                # encoding="utf-8" and errors="replace" fix Windows CP1252 issues (#138)
                 popen_kwargs = {
                     "stdin": subprocess.DEVNULL,
                     "stdout": subprocess.PIPE,
                     "stderr": subprocess.STDOUT,
                     "text": True,
+                    "encoding": "utf-8",
+                    "errors": "replace",
                     "cwd": str(AUTOCODER_ROOT),
                     "env": {**os.environ, "PYTHONUNBUFFERED": "1"},
                 }
@@ -658,11 +664,14 @@ async def _run_initializer(self) -> bool:
 
         # CREATE_NO_WINDOW on Windows prevents console window pop-ups
         # stdin=DEVNULL prevents blocking on stdin reads
+        # encoding="utf-8" and errors="replace" fix Windows CP1252 issues (#138)
         popen_kwargs = {
             "stdin": subprocess.DEVNULL,
             "stdout": subprocess.PIPE,
             "stderr": subprocess.STDOUT,
             "text": True,
+            "encoding": "utf-8",
+            "errors": "replace",
             "cwd": str(AUTOCODER_ROOT),
             "env": {**os.environ, "PYTHONUNBUFFERED": "1"},
         }
diff --git a/start.py b/start.py
index a230d13b..bc1c6263 100644
--- a/start.py
+++ b/start.py
@@ -231,7 +231,9 @@ def run_spec_creation(project_dir: Path) -> bool:
             check=False,  # Don't raise on non-zero exit
             cwd=str(Path(__file__).parent),  # Run from project root
             stderr=subprocess.PIPE,
-            text=True
+            text=True,
+            encoding="utf-8",  # Fix Windows CP1252 encoding issue (#138)
+            errors="replace",
         )
 
         # Check for authentication errors in stderr
@@ -400,7 +402,9 @@ def run_agent(project_name: str, project_dir: Path) -> None:
             cmd,
             check=False,
             stderr=subprocess.PIPE,
-            text=True
+            text=True,
+            encoding="utf-8",  # Fix Windows CP1252 encoding issue (#138)
+            errors="replace",
         )
 
         # Check for authentication errors
diff --git a/start_ui.py b/start_ui.py
index 3e619c13..7000309a 100644
--- a/start_ui.py
+++ b/start_ui.py
@@ -127,7 +127,9 @@ def check_node() -> bool:
         result = subprocess.run(
             ["node", "--version"],
             capture_output=True,
-            text=True
+            text=True,
+            encoding="utf-8",  # Fix Windows CP1252 encoding issue (#138)
+            errors="replace",
         )
         print(f"  Node.js version: {result.stdout.strip()}")
     except Exception: