diff --git a/pagure/internal/__init__.py b/pagure/internal/__init__.py
index 0a3bca2..d76b7b8 100644
--- a/pagure/internal/__init__.py
+++ b/pagure/internal/__init__.py
@@ -296,7 +296,7 @@ def get_pull_request_ready_branch():
                 if compare_branch:
                     try:
                         com = main_walker.next()
-                        main_commits.add(com.hex)
+                        main_commits.add(com.oid.hex)
                     except StopIteration:
                         com = None
                 try:
@@ -309,22 +309,17 @@ def get_pull_request_ready_branch():
                     break
 
                 if branch_commit:
-                    tmp = set(branch_commits + [branch_commit.hex])
-                else:
-                    tmp = set(branch_commits)
-                if main_commits.intersection(tmp):
-                    break
-
-                if branch_commit:
                     branch_commits.append(branch_commit.hex)
+                if main_commits.intersection(set(branch_commits)):
+                    break
 
             # If master is ahead of branch, we need to remove the commits
-            # that are already in master
-            branch_commits = [
-                com
-                for com in branch_commits
-                if com not in main_commits
-            ]
+            # that are after the first one found in master
+            i = 0
+            for i in range(len(branch_commits)):
+                if branch_commits[i] in main_commits:
+                    break
+            branch_commits = branch_commits[:i]
 
             if branch_commits:
                 branches[branchname] = branch_commits
diff --git a/pagure/lib/git.py b/pagure/lib/git.py
index e177772..8a9b118 100644
--- a/pagure/lib/git.py
+++ b/pagure/lib/git.py
@@ -1377,7 +1377,7 @@ def diff_pull_request(
         while 1:
             try:
                 com = main_walker.next()
-                main_commits.add(com.hex)
+                main_commits.add(com.oid.hex)
             except StopIteration:
                 com = None
 
@@ -1392,19 +1392,17 @@ def diff_pull_request(
 
             if branch_commit:
                 branch_commits.add(branch_commit.oid.hex)
+                diff_commits.append(branch_commit)
             if main_commits.intersection(branch_commits):
                 break
 
-            if branch_commit:
-                diff_commits.append(branch_commit)
-
         # If master is ahead of branch, we need to remove the commits
-        # that are already in master
-        diff_commits = [
-            com
-            for com in diff_commits
-            if com.oid.hex not in main_commits
-        ]
+        # that are after the first one found in master
+        i = 0
+        for i in range(len(diff_commits)):
+            if diff_commits[i].oid.hex in main_commits:
+                break
+        diff_commits = diff_commits[:i]
 
         if request.status and diff_commits:
             first_commit = repo_obj[diff_commits[-1].oid.hex]
diff --git a/pagure/ui/fork.py b/pagure/ui/fork.py
index 8338e93..75d4818 100644
--- a/pagure/ui/fork.py
+++ b/pagure/ui/fork.py
@@ -96,7 +96,7 @@ def _get_pr_info(repo_obj, orig_repo, branch_from, branch_to):
         while 1:
             try:
                 com = main_walker.next()
-                main_commits.add(com.hex)
+                main_commits.add(com.oid.hex)
             except StopIteration:
                 com = None
 
@@ -111,19 +111,17 @@ def _get_pr_info(repo_obj, orig_repo, branch_from, branch_to):
 
             if branch_commit:
                 branch_commits.add(branch_commit.oid.hex)
+                diff_commits.append(branch_commit)
             if main_commits.intersection(branch_commits):
                 break
 
-            if branch_commit:
-                diff_commits.append(branch_commit)
-
         # If master is ahead of branch, we need to remove the commits
-        # that are already in master
-        diff_commits = [
-            com
-            for com in diff_commits
-            if com.oid.hex not in main_commits
-        ]
+        # that are after the first one found in master
+        i = 0
+        for i in range(len(diff_commits)):
+            if diff_commits[i].oid.hex in main_commits:
+                break
+        diff_commits = diff_commits[:i]
 
         if diff_commits:
             first_commit = repo_obj[diff_commits[-1].oid.hex]