diff --git a/mozilla/security/nss/lib/sqlite/config.mk b/mozilla/security/nss/lib/sqlite/config.mk
index 3971b9f03b5..c7b93ed3910 100644
--- a/mozilla/security/nss/lib/sqlite/config.mk
+++ b/mozilla/security/nss/lib/sqlite/config.mk
@@ -35,11 +35,13 @@ ifeq ($(OS_TARGET),Darwin)
 # version numbers, so we use the same to be compatible.
 DARWIN_DYLIB_VERSIONS = -compatibility_version 9 -current_version 9.6
 
-# Required for Mac OSX 10.4 PowerPC, see bug 820374
+# The SQLite code that uses the Apple zone allocator calls
+# OSAtomicCompareAndSwapPtrBarrier, which is only available on Mac OS X 10.5
+# (Darwin 9.0) and later. Define SQLITE_WITHOUT_ZONEMALLOC to disable
+# that code for older versions of Mac OS X. See bug 820374.
 DARWIN_VER_MAJOR := $(shell uname -r | cut -f1 -d.)
 DARWIN_LT_9 := $(shell [ $(DARWIN_VER_MAJOR) -lt 9 ] && echo true)
 ifeq ($(DARWIN_LT_9),true)
 OS_CFLAGS += -DSQLITE_WITHOUT_ZONEMALLOC
 endif
-
-endif
+endif # Darwin