Allow '//'-style comments in #defines.
diff --git a/libacc/acc.cpp b/libacc/acc.cpp
index 6c03657..475e308 100644
--- a/libacc/acc.cpp
+++ b/libacc/acc.cpp
@@ -3821,8 +3821,20 @@
             inp();
         }
         String value;
+        bool appendToValue = true;
         while (ch != '\n' && ch != EOF) {
-            value.append(ch);
+            // Check for '//' comments.
+            if (appendToValue && ch == '/') {
+                inp();
+                if (ch == '/') {
+                    appendToValue = false;
+                } else {
+                    value.append('/');
+                }
+            }
+            if (appendToValue && ch != EOF) {
+                value.append(ch);
+            }
             inp();
         }
         char* pDefn = (char*)mGlobalArena.alloc(value.len() + 1);