diff --git a/pkgs/build-support/dotnet/build-dotnet-module/hooks/dotnet-fixup-hook.sh b/pkgs/build-support/dotnet/build-dotnet-module/hooks/dotnet-fixup-hook.sh
index 60e1e327274a..8d4315350ad5 100644
--- a/pkgs/build-support/dotnet/build-dotnet-module/hooks/dotnet-fixup-hook.sh
+++ b/pkgs/build-support/dotnet/build-dotnet-module/hooks/dotnet-fixup-hook.sh
@@ -97,5 +97,5 @@ dotnetFixupHook() {
 }
 
 if [[ -z "${dontFixup-}" && -z "${dontDotnetFixup-}" ]]; then
-    preFixupPhases+=" dotnetFixupHook"
+    appendToVar preFixupPhases dotnetFixupHook
 fi
diff --git a/pkgs/build-support/setup-hooks/wrap-gapps-hook/wrap-gapps-hook.sh b/pkgs/build-support/setup-hooks/wrap-gapps-hook/wrap-gapps-hook.sh
index 0acf4a8e6f8d..b2e52f574a52 100644
--- a/pkgs/build-support/setup-hooks/wrap-gapps-hook/wrap-gapps-hook.sh
+++ b/pkgs/build-support/setup-hooks/wrap-gapps-hook/wrap-gapps-hook.sh
@@ -34,7 +34,7 @@ gappsWrapperArgsHook() {
     done
 }
 
-preFixupPhases+=" gappsWrapperArgsHook"
+appendToVar preFixupPhases gappsWrapperArgsHook
 
 wrapGApp() {
     local program="$1"
diff --git a/pkgs/by-name/de/desktop-file-utils/setup-hook.sh b/pkgs/by-name/de/desktop-file-utils/setup-hook.sh
index 728070e34581..af6b3fab34ee 100644
--- a/pkgs/by-name/de/desktop-file-utils/setup-hook.sh
+++ b/pkgs/by-name/de/desktop-file-utils/setup-hook.sh
@@ -3,4 +3,4 @@ mimeinfoPreFixupPhase() {
     rm -f $out/share/applications/mimeinfo.cache
 }
 
-preFixupPhases="${preFixupPhases-} mimeinfoPreFixupPhase"
+appendToVar preFixupPhases mimeinfoPreFixupPhase
diff --git a/pkgs/development/ada-modules/gprbuild/gpr-project-darwin-rpath-hook.sh b/pkgs/development/ada-modules/gprbuild/gpr-project-darwin-rpath-hook.sh
index 73be2eb5960a..d20895fd12ba 100644
--- a/pkgs/development/ada-modules/gprbuild/gpr-project-darwin-rpath-hook.sh
+++ b/pkgs/development/ada-modules/gprbuild/gpr-project-darwin-rpath-hook.sh
@@ -7,4 +7,4 @@ fixGprProjectDarwinRpath() {
     done
 }
 
-preFixupPhases+=" fixGprProjectDarwinRpath"
+appendToVar preFixupPhases fixGprProjectDarwinRpath
diff --git a/pkgs/development/libraries/gtk/hooks/drop-icon-theme-cache.sh b/pkgs/development/libraries/gtk/hooks/drop-icon-theme-cache.sh
index f28a856c4f50..0762285843eb 100644
--- a/pkgs/development/libraries/gtk/hooks/drop-icon-theme-cache.sh
+++ b/pkgs/development/libraries/gtk/hooks/drop-icon-theme-cache.sh
@@ -16,4 +16,4 @@ dropIconThemeCache() {
     fi
 }
 
-preFixupPhases="${preFixupPhases-} dropIconThemeCache"
+appendToVar preFixupPhases dropIconThemeCache
diff --git a/pkgs/development/libraries/qt-5/hooks/wrap-qt-apps-hook.sh b/pkgs/development/libraries/qt-5/hooks/wrap-qt-apps-hook.sh
index 94df0a1a8e66..413368268aa2 100644
--- a/pkgs/development/libraries/qt-5/hooks/wrap-qt-apps-hook.sh
+++ b/pkgs/development/libraries/qt-5/hooks/wrap-qt-apps-hook.sh
@@ -65,7 +65,7 @@ qtOwnPathsHook() {
     qtHostPathHook "${!outputBin}"
 }
 
-preFixupPhases+=" qtOwnPathsHook"
+appendToVar preFixupPhases qtOwnPathsHook
 
 # Note: $qtWrapperArgs still gets defined even if ${dontWrapQtApps-} is set.
 wrapQtAppsHook() {
diff --git a/pkgs/development/libraries/qt-6/hooks/wrap-qt-apps-hook.sh b/pkgs/development/libraries/qt-6/hooks/wrap-qt-apps-hook.sh
index 2d858055693c..39b8635e264d 100644
--- a/pkgs/development/libraries/qt-6/hooks/wrap-qt-apps-hook.sh
+++ b/pkgs/development/libraries/qt-6/hooks/wrap-qt-apps-hook.sh
@@ -63,7 +63,7 @@ if [[ -z "${__nix_wrapQtAppsHook-}" ]]; then
         qtHostPathHook "${!outputBin}"
     }
 
-    preFixupPhases+=" qtOwnPathsHook"
+    appendToVar preFixupPhases qtOwnPathsHook
 
     # Note: $qtWrapperArgs still gets defined even if ${dontWrapQtApps-} is set.
     wrapQtAppsHook() {