diff --git a/src/com/yahoo/platform/yui/compressor/CssCompressor.java b/src/com/yahoo/platform/yui/compressor/CssCompressor.java
index 170d028..798e689 100644
--- a/src/com/yahoo/platform/yui/compressor/CssCompressor.java
+++ b/src/com/yahoo/platform/yui/compressor/CssCompressor.java
@@ -240,12 +240,17 @@ public void compress(Writer out, int linebreakpos)
         m = p.matcher(css);
         sb = new StringBuffer();
         while (m.find()) {
-            // Test for AABBCC pattern
-            if (m.group(3).equalsIgnoreCase(m.group(4)) &&
+            if (m.group(1).equals("}")) {
+                // Likely an ID selector. Don't touch.
+                // #AABBCC is a valid ID. IDs are case-sensitive.
+                m.appendReplacement(sb, m.group());
+            } else if (m.group(3).equalsIgnoreCase(m.group(4)) &&
                     m.group(5).equalsIgnoreCase(m.group(6)) &&
                     m.group(7).equalsIgnoreCase(m.group(8))) {
+                // #AABBCC pattern
                 m.appendReplacement(sb, (m.group(1) + m.group(2) + "#" + m.group(3) + m.group(5) + m.group(7)).toLowerCase());
             } else {
+                // Any other color.
                 m.appendReplacement(sb, m.group().toLowerCase());
             }
         }
diff --git a/tests/preserve-case.css b/tests/preserve-case.css
new file mode 100644
index 0000000..d7f1550
--- /dev/null
+++ b/tests/preserve-case.css
@@ -0,0 +1,12 @@
+#AddAddressForm {
+    padding: 0;
+}
+#AddAddressForm .messageBoxNeutral {
+    padding: 0;
+}
+#FeedbackMailForm{
+    padding: 0;
+}
+#FeedbackMailForm .classe{
+    margin: 0;
+}
diff --git a/tests/preserve-case.css.min b/tests/preserve-case.css.min
new file mode 100644
index 0000000..8628faa
--- /dev/null
+++ b/tests/preserve-case.css.min
@@ -0,0 +1 @@
+#AddAddressForm{padding:0}#AddAddressForm .messageBoxNeutral{padding:0}#FeedbackMailForm{padding:0}#FeedbackMailForm .classe{margin:0}