diff --git a/app/controllers/groups/group_members_controller.rb b/app/controllers/groups/group_members_controller.rb
index 8fc234a62b11bf9660f52de6c24dc098b9503763..5919bf544685f2adccd584a1d3db9778f8d5cfda 100644
--- a/app/controllers/groups/group_members_controller.rb
+++ b/app/controllers/groups/group_members_controller.rb
@@ -22,7 +22,7 @@ class Groups::GroupMembersController < Groups::ApplicationController
   end
 
   def update
-    @group_member = @group.group_members.find(params[:id])
+    @group_member = @group.members_and_requesters.find(params[:id])
 
     return render_403 unless can?(current_user, :update_group_member, @group_member)
 
diff --git a/app/controllers/projects/project_members_controller.rb b/app/controllers/projects/project_members_controller.rb
index d925dcd21ff9e1106557de0a66db5a1f1c8668c8..5a01a59481b60ee2894ae1a34093a18ca3963c48 100644
--- a/app/controllers/projects/project_members_controller.rb
+++ b/app/controllers/projects/project_members_controller.rb
@@ -26,7 +26,7 @@ class Projects::ProjectMembersController < Projects::ApplicationController
   end
 
   def update
-    @project_member = @project.project_members.find(params[:id])
+    @project_member = @project.members_and_requesters.find(params[:id])
 
     return render_403 unless can?(current_user, :update_project_member, @project_member)
 
diff --git a/changelogs/unreleased/15832-fix-access-level-update-for-requesters.yml b/changelogs/unreleased/15832-fix-access-level-update-for-requesters.yml
new file mode 100644
index 0000000000000000000000000000000000000000..9d6c958cb3e772d39e86b6ca8c431ead53efe2cd
--- /dev/null
+++ b/changelogs/unreleased/15832-fix-access-level-update-for-requesters.yml
@@ -0,0 +1,5 @@
+---
+title: Fix error that was preventing users to change the access level of access requests for Groups or Projects
+merge_request: 15832
+author:
+type: fixed
diff --git a/spec/controllers/groups/group_members_controller_spec.rb b/spec/controllers/groups/group_members_controller_spec.rb
index 9c6d584f59b8d11a8ae18eefc69547ab9e55fa33..362d5cc45146e6d1fdb896eb05add85b764725ec 100644
--- a/spec/controllers/groups/group_members_controller_spec.rb
+++ b/spec/controllers/groups/group_members_controller_spec.rb
@@ -62,6 +62,25 @@ describe Groups::GroupMembersController do
     end
   end
 
+  describe 'PUT update' do
+    let(:requester) { create(:group_member, :access_request, group: group) }
+
+    before do
+      group.add_owner(user)
+      sign_in(user)
+    end
+
+    Gitlab::Access.options.each do |label, value|
+      it "can change the access level to #{label}" do
+        xhr :put, :update, group_member: { access_level: value },
+                           group_id: group,
+                           id: requester
+
+        expect(requester.reload.human_access).to eq(label)
+      end
+    end
+  end
+
   describe 'DELETE destroy' do
     let(:member) { create(:group_member, :developer, group: group) }
 
diff --git a/spec/controllers/projects/project_members_controller_spec.rb b/spec/controllers/projects/project_members_controller_spec.rb
index a34dc27a5eded8c659f91f51b25ef168fa052d37..290dba0610a0c306a9c3a0d6ead069f07385c62e 100644
--- a/spec/controllers/projects/project_members_controller_spec.rb
+++ b/spec/controllers/projects/project_members_controller_spec.rb
@@ -66,6 +66,26 @@ describe Projects::ProjectMembersController do
     end
   end
 
+  describe 'PUT update' do
+    let(:requester) { create(:project_member, :access_request, project: project) }
+
+    before do
+      project.add_master(user)
+      sign_in(user)
+    end
+
+    Gitlab::Access.options.each do |label, value|
+      it "can change the access level to #{label}" do
+        xhr :put, :update, project_member: { access_level: value },
+                           namespace_id: project.namespace,
+                           project_id: project,
+                           id: requester
+
+        expect(requester.reload.human_access).to eq(label)
+      end
+    end
+  end
+
   describe 'DELETE destroy' do
     let(:member) { create(:project_member, :developer, project: project) }