diff --git a/app/assets/javascripts/network/network_bundle.js b/app/assets/javascripts/network/network_bundle.js
index 42d6799c82fc956f7ec24f13ce521c9f0a6e049c..a192273a18060963f4e85258ad9ca77dd94018ad 100644
--- a/app/assets/javascripts/network/network_bundle.js
+++ b/app/assets/javascripts/network/network_bundle.js
@@ -9,6 +9,8 @@
 
 (function() {
   $(function() {
+    if (!$(".network-graph").length) return;
+
     var network_graph;
     network_graph = new Network({
       url: $(".network-graph").attr('data-url'),
diff --git a/app/controllers/projects/network_controller.rb b/app/controllers/projects/network_controller.rb
index 34318391dd909e3603ff5869dd61d336b2aae730..33a152ad34f86bdf2304a26e6afb089b4d112f1b 100644
--- a/app/controllers/projects/network_controller.rb
+++ b/app/controllers/projects/network_controller.rb
@@ -5,17 +5,29 @@ class Projects::NetworkController < Projects::ApplicationController
   before_action :require_non_empty_project
   before_action :assign_ref_vars
   before_action :authorize_download_code!
+  before_action :assign_commit
 
   def show
     @url = namespace_project_network_path(@project.namespace, @project, @ref, @options.merge(format: :json))
     @commit_url = namespace_project_commit_path(@project.namespace, @project, 'ae45ca32').gsub("ae45ca32", "%s")
 
     respond_to do |format|
-      format.html
+      format.html do
+        if @options[:extended_sha1] && !@commit
+          flash.now[:alert] = "Git revision '#{@options[:extended_sha1]}' does not exist."
+        end
+      end
 
       format.json do
         @graph = Network::Graph.new(project, @ref, @commit, @options[:filter_ref])
       end
     end
   end
+
+  def assign_commit
+    return if params[:extended_sha1].blank?
+
+    @options[:extended_sha1] = params[:extended_sha1]
+    @commit = @repo.commit(@options[:extended_sha1])
+  end
 end
diff --git a/app/views/projects/network/show.html.haml b/app/views/projects/network/show.html.haml
index 29df1bab04eed34a05db262ddb1c003275c8fa45..d8951e692421633d4695a6cbc681e07c372812d0 100644
--- a/app/views/projects/network/show.html.haml
+++ b/app/views/projects/network/show.html.haml
@@ -17,5 +17,6 @@
               = check_box_tag :filter_ref, 1, @options[:filter_ref]
               %span Begin with the selected commit
 
-    .network-graph{ data: { url: @url, commit_url: @commit_url, ref: @ref, commit_id: @commit.id } }
-      = spinner nil, true
+    - if @commit
+      .network-graph{ data: { url: @url, commit_url: @commit_url, ref: @ref, commit_id: @commit.id } }
+        = spinner nil, true
diff --git a/changelogs/unreleased/fix-404-on-network-when-entering-a-nonexistent-git-revision.yml b/changelogs/unreleased/fix-404-on-network-when-entering-a-nonexistent-git-revision.yml
new file mode 100644
index 0000000000000000000000000000000000000000..d1bc8ea2eb154a2c30f45a0b89906cce614bd0be
--- /dev/null
+++ b/changelogs/unreleased/fix-404-on-network-when-entering-a-nonexistent-git-revision.yml
@@ -0,0 +1,4 @@
+---
+title: Fix 404 on network page when entering non-existent git revision
+merge_request: 7172
+author: Hiroyuki Sato
diff --git a/features/project/network_graph.feature b/features/project/network_graph.feature
index 89a02706bd283c04fe90fd46b7c2bd8d2d712314..93c884e23c58c451f6dba531f1fe59fa234cec5f 100644
--- a/features/project/network_graph.feature
+++ b/features/project/network_graph.feature
@@ -43,4 +43,4 @@ Feature: Project Network Graph
 
   Scenario: I should fail to look for a commit
     When I look for a commit by ";"
-    Then page status code should be 404
+    Then I should see non-existent git revision error message
diff --git a/features/steps/project/network_graph.rb b/features/steps/project/network_graph.rb
index 019b3124a863d5b5d6de957750e01dd69c9dc5b3..ff9251615c930d84c146e83e15cf879c132bcf53 100644
--- a/features/steps/project/network_graph.rb
+++ b/features/steps/project/network_graph.rb
@@ -109,4 +109,8 @@ class Spinach::Features::ProjectNetworkGraph < Spinach::FeatureSteps
       find('button').click
     end
   end
+
+  step 'I should see non-existent git revision error message' do
+    expect(page).to have_selector '.flash-alert', text: "Git revision ';' does not exist."
+  end
 end
diff --git a/lib/extracts_path.rb b/lib/extracts_path.rb
index 9b74364849e5e2c6251065930a9f145140dce548..82551f1f2223767fea1b16ab48e4553fb8dab363 100644
--- a/lib/extracts_path.rb
+++ b/lib/extracts_path.rb
@@ -106,7 +106,7 @@ module ExtractsPath
   # resolved (e.g., when a user inserts an invalid path or ref).
   def assign_ref_vars
     # assign allowed options
-    allowed_options = ["filter_ref", "extended_sha1"]
+    allowed_options = ["filter_ref"]
     @options = params.select {|key, value| allowed_options.include?(key) && !value.blank? }
     @options = HashWithIndifferentAccess.new(@options)
 
@@ -114,17 +114,13 @@ module ExtractsPath
     @ref, @path = extract_ref(@id)
     @repo = @project.repository
 
-    if @options[:extended_sha1].present?
-      @commit = @repo.commit(@options[:extended_sha1])
-    else
-      @commit = @repo.commit(@ref)
+    @commit = @repo.commit(@ref)
 
-      if @path.empty? && !@commit && @id.ends_with?('.atom')
-        @id = @ref = extract_ref_without_atom(@id)
-        @commit = @repo.commit(@ref)
+    if @path.empty? && !@commit && @id.ends_with?('.atom')
+      @id = @ref = extract_ref_without_atom(@id)
+      @commit = @repo.commit(@ref)
 
-        request.format = :atom if @commit
-      end
+      request.format = :atom if @commit
     end
 
     raise InvalidPathError unless @commit