diff --git a/.github/workflows/eval.yml b/.github/workflows/eval.yml
index dd2ea029dcd6..0b576a464220 100644
--- a/.github/workflows/eval.yml
+++ b/.github/workflows/eval.yml
@@ -15,6 +15,9 @@ on:
       targetSha:
         required: true
         type: string
+      baseBranch:
+        required: true
+        type: string
       systems:
         required: true
         type: string
@@ -291,6 +294,7 @@ jobs:
       - name: Compare against the target branch
         env:
           TARGET_SHA: ${{ inputs.mergedSha }}
+          BASE_BRANCH: ${{ fromJSON(inputs.baseBranch).branch }}
         run: |
           git -C nixpkgs/trusted diff --name-only "$TARGET_SHA" \
             | jq --raw-input --slurp 'split("\n")[:-1]' > touched-files.json
@@ -299,6 +303,7 @@ jobs:
           nix-build nixpkgs/trusted/ci --arg nixpkgs ./nixpkgs/trusted-pinned -A eval.compare \
             --arg combinedDir ./combined \
             --arg touchedFilesJson ./touched-files.json \
+            --argstr baseBranch "$BASE_BRANCH" \
             --out-link comparison
 
           cat comparison/step-summary.md >> "$GITHUB_STEP_SUMMARY"
diff --git a/.github/workflows/merge-group.yml b/.github/workflows/merge-group.yml
index 6ff67aefae60..196bf3040068 100644
--- a/.github/workflows/merge-group.yml
+++ b/.github/workflows/merge-group.yml
@@ -97,6 +97,7 @@ jobs:
       artifact-prefix: ${{ inputs.artifact-prefix }}
       mergedSha: ${{ needs.prepare.outputs.mergedSha }}
       targetSha: ${{ needs.prepare.outputs.targetSha }}
+      baseBranch: ${{ needs.prepare.outputs.baseBranch }}
       systems: ${{ needs.prepare.outputs.systems }}
 
   build:
diff --git a/.github/workflows/pull-request-target.yml b/.github/workflows/pull-request-target.yml
index 8edde367c13b..d4fda08d2e01 100644
--- a/.github/workflows/pull-request-target.yml
+++ b/.github/workflows/pull-request-target.yml
@@ -110,6 +110,7 @@ jobs:
       mergedSha: ${{ needs.prepare.outputs.mergedSha }}
       headSha: ${{ github.event.pull_request.head.sha }}
       targetSha: ${{ needs.prepare.outputs.targetSha }}
+      baseBranch: ${{ needs.prepare.outputs.baseBranch }}
       systems: ${{ needs.prepare.outputs.systems }}
       testVersions: ${{ contains(fromJSON(needs.prepare.outputs.touched), 'pinned') && !contains(fromJSON(needs.prepare.outputs.headBranch).type, 'development') }}
 
diff --git a/ci/eval/compare/default.nix b/ci/eval/compare/default.nix
index 856969ee8695..183e3bab8d41 100644
--- a/ci/eval/compare/default.nix
+++ b/ci/eval/compare/default.nix
@@ -49,6 +49,7 @@ in
 {
   combinedDir,
   touchedFilesJson,
+  baseBranch,
   ownersFile ? ../../OWNERS,
 }:
 let
@@ -242,7 +243,7 @@ runCommand "compare"
       echo
       echo "# Performance comparison"
       echo
-      echo "This compares the performance of this branch against its pull request base branch (e.g., 'master')"
+      echo "This compares the performance of this branch against the \`${baseBranch}\` branch."
       echo
     } >> $out/step-summary.md
 
diff --git a/ci/eval/default.nix b/ci/eval/default.nix
index 7c0a2e9f3139..2e8bec41ca5d 100644
--- a/ci/eval/default.nix
+++ b/ci/eval/default.nix
@@ -288,6 +288,9 @@ let
       #   | jq --raw-input --slurp 'split("\n")[:-1]' > touched-files.json
       # ```
       touchedFilesJson ? builtins.toFile "touched-files.json" "[ ]",
+      # The branch the local comparison is made against; matches the `master`
+      # used in the touched-files expression above.
+      baseBranch ? "master",
     }:
     let
       diffs = symlinkJoin {
@@ -305,7 +308,7 @@ let
       };
       comparisonReport = compare {
         combinedDir = combine { diffDir = diffs; };
-        inherit touchedFilesJson;
+        inherit touchedFilesJson baseBranch;
       };
     in
     comparisonReport;