diff --git a/modules/programs/difftastic.nix b/modules/programs/difftastic.nix
index 640d61581..1898f7b7b 100644
--- a/modules/programs/difftastic.nix
+++ b/modules/programs/difftastic.nix
@@ -129,7 +129,7 @@ in
           enable = lib.mkDefault true;
           iniContent =
             let
-              difftCommand = "${lib.getExe cfg.package} ${lib.cli.toGNUCommandLineShell { } cfg.options}";
+              difftCommand = "${lib.getExe cfg.package} ${lib.cli.toCommandLineShellGNU { } cfg.options}";
             in
             mkMerge [
               {
diff --git a/tests/modules/programs/difftastic/difftastic-migration.nix b/tests/modules/programs/difftastic/difftastic-migration.nix
index a51c19601..a473db022 100644
--- a/tests/modules/programs/difftastic/difftastic-migration.nix
+++ b/tests/modules/programs/difftastic/difftastic-migration.nix
@@ -26,6 +26,6 @@
     # Git config should contain difftastic configuration (backward compatibility)
     assertFileExists home-files/.config/git/config
     assertFileContains home-files/.config/git/config '[diff]'
-    assertFileRegex home-files/.config/git/config 'external = .*/difft.*--color.*--display'
+    assertFileContains home-files/.config/git/config "external = \"@difftastic@/bin/difft '--color=always' '--display=side-by-side'\""
   '';
 }
diff --git a/tests/modules/programs/difftastic/difftastic-with-git-difftool.nix b/tests/modules/programs/difftastic/difftastic-with-git-difftool.nix
index ac6c7ec9c..23b08103b 100644
--- a/tests/modules/programs/difftastic/difftastic-with-git-difftool.nix
+++ b/tests/modules/programs/difftastic/difftastic-with-git-difftool.nix
@@ -17,9 +17,9 @@
     assertFileExists home-files/.config/git/config
     assertFileContains home-files/.config/git/config '[diff]'
     # Should have BOTH diff.external AND difftool config when diffToolMode is true
-    assertFileRegex home-files/.config/git/config 'external = .*/difft.*--color.*--display'
-    assertFileRegex home-files/.config/git/config 'tool = "difftastic"'
+    assertFileContains home-files/.config/git/config "external = \"@difftastic@/bin/difft '--color=always' '--display=side-by-side'\""
+    assertFileContains home-files/.config/git/config 'tool = "difftastic"'
     assertFileContains home-files/.config/git/config '[difftool "difftastic"]'
-    assertFileRegex home-files/.config/git/config 'cmd = .*/difft.*--color.*--display.*\$LOCAL \$REMOTE'
+    assertFileContains home-files/.config/git/config "cmd = \"@difftastic@/bin/difft '--color=always' '--display=side-by-side' \$LOCAL \$REMOTE\""
   '';
 }
diff --git a/tests/modules/programs/difftastic/difftastic-with-git-external-diff.nix b/tests/modules/programs/difftastic/difftastic-with-git-external-diff.nix
index 82c872e0a..5434c9d92 100644
--- a/tests/modules/programs/difftastic/difftastic-with-git-external-diff.nix
+++ b/tests/modules/programs/difftastic/difftastic-with-git-external-diff.nix
@@ -17,7 +17,7 @@
     assertFileExists home-files/.config/git/config
     assertFileContains home-files/.config/git/config '[diff]'
     # Should have diff.external set
-    assertFileRegex home-files/.config/git/config 'external = .*/difft.*--color.*--display'
+    assertFileContains home-files/.config/git/config "external = \"@difftastic@/bin/difft '--color=always' '--display=side-by-side'\""
     # Should NOT have difftool config when diffToolMode is explicitly false
     assertFileNotRegex home-files/.config/git/config 'tool = "difftastic"'
     assertFileNotRegex home-files/.config/git/config '\[difftool "difftastic"\]'
diff --git a/tests/modules/programs/difftastic/difftastic-with-git-integration.nix b/tests/modules/programs/difftastic/difftastic-with-git-integration.nix
index 1d05636b2..8997a2f49 100644
--- a/tests/modules/programs/difftastic/difftastic-with-git-integration.nix
+++ b/tests/modules/programs/difftastic/difftastic-with-git-integration.nix
@@ -14,7 +14,7 @@
     assertFileExists home-files/.config/git/config
     assertFileContains home-files/.config/git/config '[diff]'
     # Should have diff.external set
-    assertFileRegex home-files/.config/git/config 'external = .*/difft.*--color.*--display'
+    assertFileContains home-files/.config/git/config "external = \"@difftastic@/bin/difft '--color=always' '--display=side-by-side'\""
     # Should NOT have difftool config since diffToolMode is false
     assertFileNotRegex home-files/.config/git/config 'tool = "difftastic"'
     assertFileNotRegex home-files/.config/git/config '\[difftool "difftastic"\]'