diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 65f74cc..8d64582 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -29,6 +29,9 @@ jobs:
       - name: Verify accessible SVG contract
         run: python3 scripts/test-lint-a11y.py
 
+      - name: Verify URL SVG normalization
+        run: python3 scripts/test-build-icons-quoted-attributes.py
+
       - name: Run skin linter
         run: python3 scripts/lint-skin.py --all --baseline
 
diff --git a/scripts/build-icons.py b/scripts/build-icons.py
index b191b2a..88c9325 100644
--- a/scripts/build-icons.py
+++ b/scripts/build-icons.py
@@ -249,8 +249,10 @@ def normalize_url(raw: str) -> str:
     - inline style="fill:#..." is rewritten to a fill= attribute.
     - Inkscape layer translate() transforms are stripped (canvas offset artefact).
     """
-    vb_match = re.search(r'viewBox="([^"]+)"', raw, re.IGNORECASE)
-    viewbox = vb_match.group(1) if vb_match else "0 0 128 128"
+    vb_match = re.search(
+        r'\bviewBox\s*=\s*(["\'])(.*?)\1', raw, flags=re.IGNORECASE
+    )
+    viewbox = vb_match.group(2).strip() if vb_match else "0 0 128 128"
     inner = re.search(r"<svg\b[^>]*>(.*?)</svg>", raw, flags=re.DOTALL | re.IGNORECASE)
     if not inner:
         raise ValueError("no <svg> in payload")
@@ -261,27 +263,47 @@ def normalize_url(raw: str) -> str:
     # Strip Inkscape canvas-offset translate transforms from group wrappers
     body = re.sub(r'\btransform="translate\([^"]+\)"', '', body)
 
-    def _rewrite_fill(m: re.Match) -> str:
+    def _normalized_fill(value: str) -> str:
         """Keep white; turn everything else into currentColor."""
-        hex_val = m.group(1).lower().strip()
+        hex_val = value.lower().strip()
         if hex_val in ("#fff", "#ffffff", "white", "#fefefe", "#fdfdfd"):
             return 'fill="#fff"'
         return 'fill="currentColor"'
 
-    # Rewrite inline style="fill:#rrggbb" → standalone fill= attribute
+    # Rewrite inline style="fill:#rrggbb" → standalone fill= attribute.
     body = re.sub(
-        r'style="[^"]*fill:\s*(#[0-9a-fA-F]{3,8}|white)[^"]*"',
-        lambda m: _rewrite_fill(re.search(r'(#[0-9a-fA-F]{3,8}|white)', m.group(0))),
+        r'style\s*=\s*(["\'])(.*?)\1',
+        lambda m: (
+            _normalized_fill(fill.group(1))
+            if (fill := re.search(
+                r'\bfill\s*:\s*(#[0-9a-fA-F]{3,8}|white)\b',
+                m.group(2),
+                flags=re.IGNORECASE,
+            ))
+            else m.group(0)
+        ),
         body,
+        flags=re.IGNORECASE,
     )
-    # Rewrite standalone fill="#rrggbb" attributes
+    # Rewrite standalone fill="#rrggbb" attributes.
     body = re.sub(
-        r'\bfill="(#[0-9a-fA-F]{3,8}|white)"',
-        _rewrite_fill,
+        r'\bfill\s*=\s*(["\'])(#[0-9a-fA-F]{3,8}|white)\1',
+        lambda m: _normalized_fill(m.group(2)),
         body,
+        flags=re.IGNORECASE,
+    )
+    body = re.sub(
+        r'\bstroke\s*=\s*(["\'])#[0-9a-fA-F]{3,8}\1',
+        'stroke="currentColor"',
+        body,
+        flags=re.IGNORECASE,
+    )
+    body = re.sub(
+        r'\bfill\s*=\s*(["\'])none\1',
+        '',
+        body,
+        flags=re.IGNORECASE,
     )
-    body = re.sub(r'\bstroke="#[0-9a-fA-F]{3,8}"', 'stroke="currentColor"', body)
-    body = re.sub(r'\bfill="none"', '', body)
     body = re.sub(r"\s+", " ", body).strip()
     return (
         f'<svg aria-hidden="true" width="24" height="24" viewBox="{viewbox}" '
diff --git a/scripts/test-build-icons-quoted-attributes.py b/scripts/test-build-icons-quoted-attributes.py
new file mode 100755
index 0000000..4933e9b
--- /dev/null
+++ b/scripts/test-build-icons-quoted-attributes.py
@@ -0,0 +1,47 @@
+#!/usr/bin/env python3
+"""Regression tests for quote-independent URL SVG normalization."""
+
+from __future__ import annotations
+
+import importlib.util
+import sys
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parent.parent
+BUILD = ROOT / "scripts" / "build-icons.py"
+
+
+def load_build_module():
+    sys.dont_write_bytecode = True
+    spec = importlib.util.spec_from_file_location("diagram_design_build_icons", BUILD)
+    if spec is None or spec.loader is None:
+        raise AssertionError("could not load build-icons.py")
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
+def main() -> int:
+    build_icons = load_build_module()
+    svg = (
+        "<svg viewBox='0 0 32 16'>"
+        "<path style='fill:#123456;stroke:#654321' d='M0 0h32v16H0z'/>"
+        "<circle fill='#abcdef' stroke='#111111' cx='8' cy='8' r='4'/>"
+        "</svg>"
+    )
+    normalized = build_icons.normalize_url(svg)
+    if 'viewBox="0 0 32 16"' not in normalized:
+        raise AssertionError(f"single-quoted viewBox was not preserved: {normalized}")
+    if any(color in normalized for color in ("#123456", "#654321", "#abcdef", "#111111")):
+        raise AssertionError(f"source colors escaped normalization: {normalized}")
+    if normalized.count('fill="currentColor"') < 2:
+        raise AssertionError(f"single-quoted fills were not normalized: {normalized}")
+    if 'stroke="currentColor"' not in normalized:
+        raise AssertionError(f"single-quoted strokes were not normalized: {normalized}")
+    print("PASS: URL SVG normalization handles single-quoted attributes")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())