diff --git a/Mac/BuildScript/build-installer.py b/Mac/BuildScript/build-installer.py
index de1a980..3e728e0 100755
--- a/Mac/BuildScript/build-installer.py
+++ b/Mac/BuildScript/build-installer.py
@@ -952,7 +952,7 @@
                "--with-universal-archs=%s "
                "%s "
                "LDFLAGS='-g -L%s/libraries/usr/local/lib' "
-               "OPT='-g -O3 -I%s/libraries/usr/local/include' 2>&1"%(
+               "CFLAGS='-g -I%s/libraries/usr/local/include' 2>&1"%(
         shellQuote(os.path.join(SRCDIR, 'configure')), shellQuote(SDKPATH),
         UNIVERSALARCHS,
         (' ', '--with-computed-gotos ')[PYTHON_3],
diff --git a/Misc/NEWS b/Misc/NEWS
index 5636796..3b98031 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -289,6 +289,11 @@
   problems in the Apple-supplied Tcl/Tk 8.5 shipped in OS X 10.6
   and later releases.
 
+- Issue #19019: Change the OS X installer build script to use CFLAGS instead
+  of OPT for special build options.  By setting OPT, some compiler-specific
+  options like -fwrapv were overridden and thus not used, which could result
+  in broken interpreters when building with clang.
+
 IDLE
 ----