diff --git a/main.go b/main.go
index 3d10edf..95a7fe5 100644
--- a/main.go
+++ b/main.go
@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	git "github.com/go-git/go-git/v5"
+	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/plumbing/object"
 	gha "github.com/sethvargo/go-githubactions"
 )
@@ -37,14 +38,17 @@ func main() {
 	}
 
 	// Limit number of iterations.
-	from := gha.GetInput("from")
+	var lca *object.Commit
+	if from := gha.GetInput("from"); from != "" {
+		lca = getMergeBase(r, head, from)
+	}
 
 	// Processing result.
 	var fail bool
 
 	_ = commits.ForEach(func(c *object.Commit) error {
 		// Stop iterator when limit is reached.
-		if len(from) != 0 && strings.HasPrefix(c.ID().String(), from) {
+		if lca != nil && c.Hash == lca.Hash {
 			return errors.New("stop")
 		}
 
@@ -81,3 +85,27 @@ func main() {
 		os.Exit(1)
 	}
 }
+
+func getMergeBase(r *git.Repository, head *plumbing.Reference, from string) *object.Commit {
+	h, err := r.ResolveRevision(plumbing.Revision(from))
+	if err != nil {
+		log.Fatalf("Failed to resolve a reference: %v", err)
+	}
+
+	to, err := r.CommitObject(*h)
+	if err != nil {
+		log.Fatalf("Failed to get commit object: %v", err)
+	}
+
+	other, err := r.CommitObject(head.Hash())
+	if err != nil {
+		log.Fatalf("Failed to get HEAD commit object: %v", err)
+	}
+
+	cc, err := to.MergeBase(other)
+	if err != nil {
+		log.Fatalf("Failed to determine merge-base: %v", err)
+	}
+
+	return cc[0]
+}