diff --git a/run_tests.sh b/run_tests.sh
index d32ffd4..2cbcab6 100755
--- a/run_tests.sh
+++ b/run_tests.sh
@@ -3,11 +3,15 @@
 
 cd "$(dirname "$0")"
 
-# Use full python path if in Hermes environment
+# Default to Hermes python (has pytest), fall back to system python
 if [ -f "/opt/hermes/tools/python-3.14.9+202****1021-linux-x64/bin/python" ]; then
     PYTHON="/opt/hermes/tools/python-3.14.9+202****1021-linux-x64/bin/python"
-else
+elif command -v python3 &>/dev/null && python3 -c "import pytest" 2>/dev/null; then
     PYTHON="python3"
+else
+    echo "Error: pytest not found. Try:"
+    echo "  pip install pytest numpy psutil Pillow"
+    exit 1
 fi
 
 echo "Running tests with: $PYTHON"