diff --git a/.github/workflows/mkosi.yml b/.github/workflows/mkosi.yml
index 5cf9a0d7538..cfdfa8eba05 100644
--- a/.github/workflows/mkosi.yml
+++ b/.github/workflows/mkosi.yml
@@ -58,30 +58,37 @@ jobs:
             release: rolling
             sanitizers: ""
             llvm: 0
+            cflags: "-O2 -D_FORTIFY_SOURCE=3"
           - distro: debian
             release: testing
             sanitizers: ""
             llvm: 0
+            cflags: "-Og"
           - distro: ubuntu
             release: noble
             sanitizers: ""
             llvm: 0
+            cflags: "-Og"
           - distro: fedora
             release: "40"
             sanitizers: ""
             llvm: 0
+            cflags: "-Og"
           - distro: fedora
             release: rawhide
             sanitizers: address,undefined
             llvm: 1
+            cflags: "-Og"
           - distro: opensuse
             release: tumbleweed
             sanitizers: ""
             llvm: 0
+            cflags: "-Og"
           - distro: centos
             release: "9"
             sanitizers: ""
             llvm: 0
+            cflags: "-Og"
 
     steps:
     - uses: actions/checkout@a5ac7e51b41094c92402da3b24376905380afc29
@@ -127,8 +134,7 @@ jobs:
         Environment=
                 # Build debuginfo packages since we'll be publishing the packages as artifacts.
                 WITH_DEBUG=1
-                # Enabling optimizations significantly speeds up integration tests.
-                OPTIMIZATION=g
+                CFLAGS="${{ matrix.cflags }}"
                 SANITIZERS=${{ matrix.sanitizers }}
                 MESON_OPTIONS=--werror
                 LLVM=${{ matrix.llvm }}
diff --git a/mkosi.images/system/mkosi.conf.d/10-arch/mkosi.build.chroot b/mkosi.images/system/mkosi.conf.d/10-arch/mkosi.build.chroot
index 9407c1e053d..60b6444bfc1 100755
--- a/mkosi.images/system/mkosi.conf.d/10-arch/mkosi.build.chroot
+++ b/mkosi.images/system/mkosi.conf.d/10-arch/mkosi.build.chroot
@@ -24,7 +24,7 @@ ln --symbolic . "pkg/$ID/src"
 # shellcheck source=/dev/null
 . /etc/makepkg.conf
 
-MKOSI_CFLAGS="-O${OPTIMIZATION:-0} -Wp,-U_FORTIFY_SOURCE"
+MKOSI_CFLAGS="-Wp,-U_FORTIFY_SOURCE"
 if ((LLVM)); then
     # TODO: Remove -fno-sanitize-function when https://github.com/systemd/systemd/issues/29972 is fixed.
     MKOSI_CFLAGS="$MKOSI_CFLAGS -shared-libasan -fno-sanitize=function"
@@ -40,10 +40,10 @@ if ((WIPE)); then
     MKOSI_MESON_OPTIONS="$MKOSI_MESON_OPTIONS --wipe"
 fi
 
-# Override the default options. Disable FORTIFY_SOURCE because it doesn't work with O0. We specifically
-# disable "strip", "zipman" and "lto" as they slow down builds significantly. OPTIONS= cannot be overridden
-# on the makepkg command line so we append to /etc/makepkg.conf instead. The rootfs is overlaid with a
-# writable tmpfs during the build script so these changes don't end up in the image itself.
+# Override the default options. We specifically disable "strip", "zipman" and "lto" as they slow down builds
+# significantly. OPTIONS= cannot be overridden on the makepkg command line so we append to /etc/makepkg.conf
+# instead. The rootfs is overlaid with a writable tmpfs during the build script so these changes don't end up
+# in the image itself.
 tee --append /etc/makepkg.conf >/dev/null <<EOF
 export CC="$( ((LLVM)) && echo clang || echo gcc)"
 export CXX="$( ((LLVM)) && echo clang++ || echo g++)"
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 d2ba46bb562..31069aa8b3d 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="-O${OPTIMIZATION:-0} -Wp,-U_FORTIFY_SOURCE"
+MKOSI_CFLAGS="-Wp,-U_FORTIFY_SOURCE"
 if ((WITH_DEBUG)); then
     MKOSI_CFLAGS="$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 e36fb4887ce..1b8fe586ca2 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="-O${OPTIMIZATION:-0}"
+MKOSI_CFLAGS=""
 if ((LLVM)); then
     # TODO: Remove -fno-sanitize-function when https://github.com/systemd/systemd/issues/29972 is fixed.
     MKOSI_CFLAGS="$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 0a08e8191a9..4add69085d5 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="-O${OPTIMIZATION:-0} -Wp,-U_FORTIFY_SOURCE"
+MKOSI_CFLAGS="-Wp,-U_FORTIFY_SOURCE"
 if ((WITH_DEBUG)); then
     MKOSI_CFLAGS="$MKOSI_CFLAGS -fdebug-prefix-map=../src=$SRCDEST"
 fi