diff --git a/diff-sha.sh b/diff-sha.sh
index b6c5e9a5..7e2c0523 100644
--- a/diff-sha.sh
+++ b/diff-sha.sh
@@ -7,16 +7,11 @@ GITHUB_OUTPUT=${GITHUB_OUTPUT:-""}
 EXTRA_ARGS="--no-tags"
 PREVIOUS_SHA=""
 CURRENT_SHA=""
-MERGE_BASE_EXRTRA_ARGS=""
 
 if [[ "$GITHUB_REF" == "refs/tags/"* ]]; then
   EXTRA_ARGS=""
 fi
 
-if [[ "$GITHUB_EVENT_HEAD_REPO_FORK" == "true" ]]; then
-  MERGE_BASE_EXRTRA_ARGS="--fork-point"
-fi
-
 echo "::group::changed-files-diff-sha"
 
 if [[ -n $INPUT_PATH ]]; then
@@ -68,9 +63,9 @@ if [[ -z $GITHUB_BASE_REF ]]; then
     if [[ -z $INPUT_SHA ]]; then
       CURRENT_SHA=$(git rev-list -n 1 HEAD 2>&1) && exit_status=$? || exit_status=$?
     else
-      CURRENT_SHA=$INPUT_SHA; exit_status=$?
       # shellcheck disable=SC2086
-      git fetch $EXTRA_ARGS -u --progress --deepen="$INPUT_FETCH_DEPTH" origin +"$GITHUB_REF":refs/remotes/origin/"$CURRENT_BRANCH" 2>&1 && exit_status=$? || exit_status=$?
+      git fetch $EXTRA_ARGS -u --progress --deepen="$INPUT_FETCH_DEPTH"
+      CURRENT_SHA=$INPUT_SHA; exit_status=$?
     fi
   fi
 
@@ -131,9 +126,9 @@ if [[ -z $GITHUB_BASE_REF ]]; then
       fi
     fi
   else
-    PREVIOUS_SHA=$INPUT_BASE_SHA
     # shellcheck disable=SC2086
-    git fetch $EXTRA_ARGS -u --progress --deepen="$INPUT_FETCH_DEPTH" origin +"$GITHUB_REF":refs/remotes/origin/"$CURRENT_BRANCH" 2>&1 && exit_status=$? || exit_status=$?
+    git fetch $EXTRA_ARGS -u --progress --deepen="$INPUT_FETCH_DEPTH"
+    PREVIOUS_SHA=$INPUT_BASE_SHA
   fi
 
   echo "::debug::Target branch $TARGET_BRANCH..."
@@ -204,7 +199,7 @@ else
         PREVIOUS_SHA=$(git rev-parse origin/"$CURRENT_BRANCH" 2>&1) && exit_status=$? || exit_status=$?
       fi
     else
-      PREVIOUS_SHA=$(git merge-base $MERGE_BASE_EXRTRA_ARGS "$TARGET_BRANCH" "$CURRENT_SHA" 2>&1) && exit_status=$? || exit_status=$?
+      PREVIOUS_SHA=$(git merge-base "$TARGET_BRANCH" "$CURRENT_SHA" 2>&1) && exit_status=$? || exit_status=$?
 
       if [[ -z "$PREVIOUS_SHA" ]]; then
         PREVIOUS_SHA=$GITHUB_EVENT_PULL_REQUEST_BASE_SHA && exit_status=$? || exit_status=$?
@@ -230,7 +225,7 @@ else
           # shellcheck disable=SC2086
           git fetch $EXTRA_ARGS -u --progress --deepen="$depth" origin +"$GITHUB_REF":refs/remotes/origin/"$CURRENT_BRANCH"
 
-          PREVIOUS_SHA=$(git merge-base $MERGE_BASE_EXRTRA_ARGS "$TARGET_BRANCH" "$CURRENT_SHA" 2>&1) && exit_status=$? || exit_status=$?
+          PREVIOUS_SHA=$(git merge-base "$TARGET_BRANCH" "$CURRENT_SHA" 2>&1) && exit_status=$? || exit_status=$?
 
           if [[ $depth -gt $max_depth ]]; then
             echo "::error::Unable to locate a common ancestor between $TARGET_BRANCH and $CURRENT_SHA"