diff --git a/conf.d/forgit.plugin.fish b/conf.d/forgit.plugin.fish
index 4a98d02..c8b9203 100644
--- a/conf.d/forgit.plugin.fish
+++ b/conf.d/forgit.plugin.fish
@@ -21,6 +21,15 @@ function forgit::reverse_lines
     end
 end
 
+function forgit::previous_commit
+    # "SHA~" is invalid when the commit is the first commit, but we can use "--root" instead
+    if test (git rev-parse $argv) = (git rev-list --max-parents=0 HEAD)
+        echo "--root"
+    else
+        echo "$argv~"
+    end
+end
+
 # extract the first git sha occuring in the input and strip trailing newline
 set -g forgit_extract_sha  "grep -Eo '[a-f0-9]+' | head -1 | tr -d '[:space:]'"
 
@@ -399,11 +408,7 @@ function forgit::fixup -d "git fixup"
     set target_commit (eval "$cmd" | FZF_DEFAULT_OPTS="$opts" fzf | eval "$forgit_extract_sha")
 
     if test -n "$target_commit" && git commit --fixup "$target_commit"
-        # "$target_commit~" is invalid when the commit is the first commit, but we can use "--root" instead
-        set prev_commit "$target_commit~"
-        if test "(git rev-parse '$target_commit')" = "(git rev-list --max-parents=0 HEAD)"
-            set prev_commit "--root"
-        end
+        set prev_commit (forgit::previous_commit $target_commit)
 
         GIT_SEQUENCE_EDITOR=: git rebase --autostash -i --autosquash "$prev_commit"
     end
@@ -437,10 +442,12 @@ function forgit::rebase -d "git rebase"
         --preview=\"$preview\"
         $FORGIT_REBASE_FZF_OPTS
     "
-    set commit (eval "$cmd" | FZF_DEFAULT_OPTS="$opts" fzf | eval "$forgit_extract_sha")
+    set target_commit (eval "$cmd" | FZF_DEFAULT_OPTS="$opts" fzf | eval "$forgit_extract_sha")
 
-    if test $commit
-        git rebase -i "$commit"
+    if test $target_commit
+        set prev_commit (forgit::previous_commit $target_commit)
+
+        git rebase -i "$prev_commit"
     end
 end
 
diff --git a/forgit.plugin.zsh b/forgit.plugin.zsh
index 55556fa..9e0e301 100755
--- a/forgit.plugin.zsh
+++ b/forgit.plugin.zsh
@@ -6,6 +6,15 @@ forgit::inside_work_tree() { git rev-parse --is-inside-work-tree >/dev/null; }
 # tac is not available on OSX, tail -r is not available on Linux, so we use either of them
 forgit::reverse_lines() { tac 2> /dev/null || tail -r; }
 
+forgit::previous_commit() {
+    # "SHA~" is invalid when the commit is the first commit, but we can use "--root" instead
+    if [[ "$(git rev-parse "$1")" == "$(git rev-list --max-parents=0 HEAD)" ]]; then
+        echo "--root"
+    else
+        echo "$1~"
+    fi
+}
+
 # optional render emoji characters (https://github.com/wfxr/emoji-cli)
 hash emojify &>/dev/null && forgit_emojify='|emojify'
 
@@ -177,7 +186,7 @@ forgit::cherry::pick() {
 
 forgit::rebase() {
     forgit::inside_work_tree || return 1
-    local cmd preview opts graph files commit
+    local cmd preview opts graph files target_commit prev_commit
     graph=--graph
     [[ $FORGIT_LOG_GRAPH_ENABLE == false ]] && graph=
     cmd="git log $graph --color=always --format='$forgit_log_format' $* $forgit_emojify"
@@ -190,8 +199,12 @@ forgit::rebase() {
         --preview=\"$preview\"
         $FORGIT_REBASE_FZF_OPTS
     "
-    commit=$(eval "$cmd" | FZF_DEFAULT_OPTS="$opts" fzf | eval "$forgit_extract_sha")
-    [[ -n "$commit" ]] && git rebase -i "$commit"
+    target_commit=$(eval "$cmd" | FZF_DEFAULT_OPTS="$opts" fzf | eval "$forgit_extract_sha")
+    if [[ -n "$target_commit" ]]; then
+        prev_commit=$(forgit::previous_commit $target_commit)
+
+        git rebase -i "$prev_commit"
+    fi
 }
 
 forgit::fixup() {
@@ -212,12 +225,7 @@ forgit::fixup() {
     "
     target_commit=$(eval "$cmd" | FZF_DEFAULT_OPTS="$opts" fzf | eval "$forgit_extract_sha")
     if [[ -n "$target_commit" ]] && git commit --fixup "$target_commit"; then
-        # "$target_commit~" is invalid when the commit is the first commit, but we can use "--root" instead
-        if [[ "$(git rev-parse "$target_commit")" == "$(git rev-list --max-parents=0 HEAD)" ]]; then
-            prev_commit="--root"
-        else
-            prev_commit="$target_commit~"
-        fi
+        prev_commit=$(forgit::previous_commit $target_commit)
         # rebase will fail if there are unstaged changes so --autostash is needed to temporarily stash them
         # GIT_SEQUENCE_EDITOR=: is needed to skip the editor
         GIT_SEQUENCE_EDITOR=: git rebase --autostash -i --autosquash "$prev_commit"