diff --git a/extra/thunderbird/PKGBUILD b/extra/thunderbird/PKGBUILD
index f945ce7aa..3d07bb140 100644
--- a/extra/thunderbird/PKGBUILD
+++ b/extra/thunderbird/PKGBUILD
@@ -14,7 +14,7 @@ highmem=1
 pkgbase=thunderbird
 pkgname=(thunderbird)
 pkgver=115.2.0
-pkgrel=3
+pkgrel=4
 pkgdesc='Standalone mail and news reader from mozilla.org'
 url='https://www.thunderbird.net/'
 arch=(x86_64)
@@ -141,6 +141,11 @@ build() {
   fi
   export MACH_BUILD_PYTHON_NATIVE_PACKAGE_SOURCE=none
   export MOZBUILD_STATE_PATH="${srcdir}/mozbuild"
+
+  # malloc_usable_size is used in various parts of the codebase
+  CFLAGS="${CFLAGS/_FORTIFY_SOURCE=3/_FORTIFY_SOURCE=2}"
+  CXXFLAGS="${CXXFLAGS/_FORTIFY_SOURCE=3/_FORTIFY_SOURCE=2}"
+
   ./mach configure
   ./mach build
   ./mach buildsymbols