diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index cf9926b4da..1adee669eb 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -542,7 +542,7 @@ gimp-snap:
   before_script:
     - if (-not $env:MSYSTEM_PREFIX) { $env:MSYSTEM_PREFIX = if ((Get-WmiObject Win32_ComputerSystem).SystemType -like 'ARM64*') { 'clangarm64' } else { 'clang64' }}
     # FIXME:'gimpenv' have buggy code about Windows paths. See: https://gitlab.gnome.org/GNOME/gimp/-/issues/12284
-    - $GIMP_PREFIX = "$PWD\_install-$env:MSYSTEM_PREFIX".Replace('\', '/')
+    - $GIMP_PREFIX = "$PWD\_install-$env:MSYSTEM_PREFIX"
   timeout: 30m
 
 .win_environ: &WIN_ENVIRON
diff --git a/build/windows/2_build-gimp-msys2.ps1 b/build/windows/2_build-gimp-msys2.ps1
index 4925bc8dc8..6a39dc363d 100644
--- a/build/windows/2_build-gimp-msys2.ps1
+++ b/build/windows/2_build-gimp-msys2.ps1
@@ -33,7 +33,7 @@ if ($GITLAB_CI)
 if (-not $GIMP_PREFIX)
   {
     #FIXME:'gimpenv' have buggy code about Windows paths. See: https://gitlab.gnome.org/GNOME/gimp/-/issues/12284
-    $GIMP_PREFIX = "$PWD\..\_install".Replace('\', '/')
+    $GIMP_PREFIX = "$PWD\..\_install"
   }
 Invoke-Expression ((Get-Content .gitlab-ci.yml | Select-String 'win_environ\[' -Context 0,7) -replace '> ','' -replace '- ','')
 
diff --git a/meson.build b/meson.build
index 0196279053..1ea94b5374 100644
--- a/meson.build
+++ b/meson.build
@@ -128,7 +128,7 @@ fs        = import('fs')
 
 cc        = meson.get_compiler('c')
 cxx       = meson.get_compiler('cpp')
-prefix    = get_option('prefix')
+prefix    = get_option('prefix').replace('\\', '/')
 buildtype = get_option('buildtype')
 exec_ver  = '-' + gimp_app_version