diff --git a/mkosi.images/system/mkosi.conf.d/10-arch/mkosi.build.chroot b/mkosi.images/system/mkosi.conf.d/10-arch/mkosi.build.chroot
index 60b6444bfc..7c862d527c 100755
--- a/mkosi.images/system/mkosi.conf.d/10-arch/mkosi.build.chroot
+++ b/mkosi.images/system/mkosi.conf.d/10-arch/mkosi.build.chroot
@@ -24,7 +24,7 @@ ln --symbolic . "pkg/$ID/src"
 # shellcheck source=/dev/null
 . /etc/makepkg.conf
 
-MKOSI_CFLAGS="-Wp,-U_FORTIFY_SOURCE"
+MKOSI_CFLAGS="-O0 -Wp,-U_FORTIFY_SOURCE"
 if ((LLVM)); then
     # TODO: Remove -fno-sanitize-function when https://github.com/systemd/systemd/issues/29972 is fixed.
     MKOSI_CFLAGS="$MKOSI_CFLAGS -shared-libasan -fno-sanitize=function"
diff --git a/mkosi.images/system/mkosi.conf.d/10-centos-fedora/mkosi.build.chroot b/mkosi.images/system/mkosi.conf.d/10-centos-fedora/mkosi.build.chroot
index 31069aa8b3..2c05787654 100755
--- a/mkosi.images/system/mkosi.conf.d/10-centos-fedora/mkosi.build.chroot
+++ b/mkosi.images/system/mkosi.conf.d/10-centos-fedora/mkosi.build.chroot
@@ -47,7 +47,7 @@ COMMON_MACRO_OVERRIDES=(
 )
 
 # TODO: Drop -U_FORTIFY_SOURCE when we switch to CentOS Stream 10.
-MKOSI_CFLAGS="-Wp,-U_FORTIFY_SOURCE"
+MKOSI_CFLAGS="-O0 -Wp,-U_FORTIFY_SOURCE"
 if ((WITH_DEBUG)); then
     MKOSI_CFLAGS="$MKOSI_CFLAGS -fdebug-prefix-map=../src=$SRCDEST"
 fi
diff --git a/mkosi.images/system/mkosi.conf.d/10-debian-ubuntu/mkosi.build.chroot b/mkosi.images/system/mkosi.conf.d/10-debian-ubuntu/mkosi.build.chroot
index 1b8fe586ca..7e4eab9940 100755
--- a/mkosi.images/system/mkosi.conf.d/10-debian-ubuntu/mkosi.build.chroot
+++ b/mkosi.images/system/mkosi.conf.d/10-debian-ubuntu/mkosi.build.chroot
@@ -44,7 +44,7 @@ EOF
 cat debian/changelog >>debian/changelog.new
 mv debian/changelog.new debian/changelog
 
-MKOSI_CFLAGS=""
+MKOSI_CFLAGS="-O0"
 if ((LLVM)); then
     # TODO: Remove -fno-sanitize-function when https://github.com/systemd/systemd/issues/29972 is fixed.
     MKOSI_CFLAGS="$MKOSI_CFLAGS -shared-libasan -fno-sanitize=function"
diff --git a/mkosi.images/system/mkosi.conf.d/10-opensuse/mkosi.build.chroot b/mkosi.images/system/mkosi.conf.d/10-opensuse/mkosi.build.chroot
index 4add69085d..3d6cc58b64 100755
--- a/mkosi.images/system/mkosi.conf.d/10-opensuse/mkosi.build.chroot
+++ b/mkosi.images/system/mkosi.conf.d/10-opensuse/mkosi.build.chroot
@@ -42,7 +42,7 @@ DIST="$(rpm --eval %dist)"
 ARCH="$(rpm --eval %_arch)"
 SRCDEST="/usr/src/debug/systemd-$VERSION-${RELEASE}${DIST}.$ARCH"
 
-MKOSI_CFLAGS="-Wp,-U_FORTIFY_SOURCE"
+MKOSI_CFLAGS="-O0 -Wp,-U_FORTIFY_SOURCE"
 if ((WITH_DEBUG)); then
     MKOSI_CFLAGS="$MKOSI_CFLAGS -fdebug-prefix-map=../src=$SRCDEST"
 fi