diff --git a/entrypoint.sh b/entrypoint.sh
index b9c200f7..cfd58d00 100755
--- a/entrypoint.sh
+++ b/entrypoint.sh
@@ -1,20 +1,44 @@
 #!/bin/bash
 set -e
 
+if [ -n "$MAGICK_MAX_WIDTH" ]; then
+  if ! [[ "$MAGICK_MAX_WIDTH" =~ ^[0-9]+$ ]]; then
+    echo "Error: MAGICK_MAX_WIDTH must be a positive integer in pixels" >&2
+    exit 1
+  fi
+fi
+
+if [ -n "$MAGICK_MAX_HEIGHT" ]; then
+  if ! [[ "$MAGICK_MAX_HEIGHT" =~ ^[0-9]+$ ]]; then
+    echo "Error: MAGICK_MAX_HEIGHT must be a positive integer in pixels" >&2
+    exit 1
+  fi
+fi
+
 if [ -n "$MAGICK_MAX_WIDTH" ] || [ -n "$MAGICK_MAX_HEIGHT" ]; then
   POLICY_DIR="/etc/ImageMagick-7"
   POLICY_FILE="$POLICY_DIR/policy.xml"
 
-  mkdir -p "$POLICY_DIR"
-
-  echo "<policymap>" > "$POLICY_FILE"
-  if [ -n "$MAGICK_MAX_WIDTH" ]; then
-    echo "  <policy domain=\"resource\" name=\"width\" value=\"$MAGICK_MAX_WIDTH\"/>" >> "$POLICY_FILE"
+  if [ -f "$POLICY_FILE" ] && grep -q "</policymap>" "$POLICY_FILE"; then
+    [ -n "$MAGICK_MAX_WIDTH" ] && sed -i '/<policy domain="resource" name="width"/d' "$POLICY_FILE"
+    [ -n "$MAGICK_MAX_HEIGHT" ] && sed -i '/<policy domain="resource" name="height"/d' "$POLICY_FILE"
+    if [ -n "$MAGICK_MAX_WIDTH" ]; then
+      sed -i "s|</policymap>|  <policy domain=\"resource\" name=\"width\" value=\"$MAGICK_MAX_WIDTH\"/>\n</policymap>|" "$POLICY_FILE"
+    fi
+    if [ -n "$MAGICK_MAX_HEIGHT" ]; then
+      sed -i "s|</policymap>|  <policy domain=\"resource\" name=\"height\" value=\"$MAGICK_MAX_HEIGHT\"/>\n</policymap>|" "$POLICY_FILE"
+    fi
+  else
+    mkdir -p "$POLICY_DIR"
+    echo "<policymap>" > "$POLICY_FILE"
+    if [ -n "$MAGICK_MAX_WIDTH" ]; then
+      echo "  <policy domain=\"resource\" name=\"width\" value=\"$MAGICK_MAX_WIDTH\"/>" >> "$POLICY_FILE"
+    fi
+    if [ -n "$MAGICK_MAX_HEIGHT" ]; then
+      echo "  <policy domain=\"resource\" name=\"height\" value=\"$MAGICK_MAX_HEIGHT\"/>" >> "$POLICY_FILE"
+    fi
+    echo "</policymap>" >> "$POLICY_FILE"
   fi
-  if [ -n "$MAGICK_MAX_HEIGHT" ]; then
-    echo "  <policy domain=\"resource\" name=\"height\" value=\"$MAGICK_MAX_HEIGHT\"/>" >> "$POLICY_FILE"
-  fi
-  echo "</policymap>" >> "$POLICY_FILE"
 fi
 
 exec bun run dist/src/index.js