diff --git a/compiler-rt/lib/scudo/standalone/combined.h b/compiler-rt/lib/scudo/standalone/combined.h
--- a/compiler-rt/lib/scudo/standalone/combined.h
+++ b/compiler-rt/lib/scudo/standalone/combined.h
@@ -279,15 +279,18 @@
 
   uptr computeOddEvenMaskForPointerMaybe(Options Options, uptr Ptr,
                                          uptr ClassId) {
+    const uptr Tag = 1; // Always exclude Tag 0 is may be used for headers.
     if (!Options.get(OptionBit::UseOddEvenTags))
-      return 0;
+      return Tag;
 
     // If a chunk's tag is odd, we want the tags of the surrounding blocks to be
     // even, and vice versa. Blocks are laid out Size bytes apart, and adding
     // Size to Ptr will flip the least significant set bit of Size in Ptr, so
     // that bit will have the pattern 010101... for consecutive blocks, which we
     // can use to determine which tag mask to use.
-    return 0x5555U << ((Ptr >> SizeClassMap::getSizeLSBByClassId(ClassId)) & 1);
+    return Tag |
+           (0x5555U << ((Ptr >> SizeClassMap::getSizeLSBByClassId(ClassId)) &
+                        1));
   }
 
   NOINLINE void *allocate(uptr Size, Chunk::Origin Origin,