diff --git a/lib/gush/cli.rb b/lib/gush/cli.rb
index 7244ca5..c54b804 100644
--- a/lib/gush/cli.rb
+++ b/lib/gush/cli.rb
@@ -74,9 +74,7 @@ def rm(workflow_id)
     option :start, type: :numeric, default: nil
     option :stop, type: :numeric, default: nil
     def list(start=nil, stop=nil)
-      workflows = client.workflow_ids(start, stop).map do |id|
-        client.find_workflow(id)
-      end
+      workflows = client.workflows(start, stop)
 
       rows = workflows.map do |workflow|
         [workflow.id, (Time.at(workflow.started_at) if workflow.started_at), workflow.class, {alignment: :center, value: status_for(workflow)}]
diff --git a/lib/gush/client.rb b/lib/gush/client.rb
index 144f25d..27011e5 100644
--- a/lib/gush/client.rb
+++ b/lib/gush/client.rb
@@ -104,7 +104,11 @@ def workflow_ids(start=nil, stop=nil, by_ts: false, order: :asc)
     end
 
     def workflows(start=nil, stop=nil, **kwargs)
-      workflow_ids(start, stop, **kwargs).map { |id| find_workflow(id) }
+      workflow_ids(start, stop, **kwargs).map do |id|
+        find_workflow(id)
+        rescue WorkflowClassDoesNotExist, JobClassDoesNotExist
+          nil
+      end.compact
     end
 
     def workflows_count
@@ -285,6 +289,8 @@ def workflow_from_hash(hash, nodes = [])
         globals: hash[:globals],
         internal_state: internal_state
       )
+    rescue NameError
+      raise WorkflowClassDoesNotExist.new("Workflow #{hash[:klass]} doesn't exist")
     end
 
     def redis
diff --git a/lib/gush/errors.rb b/lib/gush/errors.rb
index 6c65936..db7f5da 100644
--- a/lib/gush/errors.rb
+++ b/lib/gush/errors.rb
@@ -1,4 +1,6 @@
 module Gush
   class WorkflowNotFound < StandardError; end
+  class WorkflowClassDoesNotExist < StandardError; end
+  class JobClassDoesNotExist < StandardError; end
   class DependencyLevelTooDeep < StandardError; end
 end
diff --git a/lib/gush/job.rb b/lib/gush/job.rb
index 9c0c962..ae1d3da 100644
--- a/lib/gush/job.rb
+++ b/lib/gush/job.rb
@@ -38,6 +38,8 @@ def to_json(options = {})
 
     def self.from_hash(hash)
       hash[:klass].constantize.new(hash)
+    rescue NameError
+      raise JobClassDoesNotExist.new("Job #{hash[:klass]} doesn't exist")
     end
 
     def output(data)
diff --git a/spec/gush/job_spec.rb b/spec/gush/job_spec.rb
index eb3a971..29d8d09 100644
--- a/spec/gush/job_spec.rb
+++ b/spec/gush/job_spec.rb
@@ -165,5 +165,11 @@
       expect(job.started_at).to eq(55)
       expect(job.enqueued_at).to eq(444)
     end
+
+    it "raises JobClassDoesNotExist if the job class is no longer defined" do
+      expect {
+        described_class.from_hash({klass: 'NonExistentJob'})
+      }.to raise_error(Gush::JobClassDoesNotExist)
+    end
   end
 end
diff --git a/spec/gush/workflow_spec.rb b/spec/gush/workflow_spec.rb
index d3a385d..efae2ef 100644
--- a/spec/gush/workflow_spec.rb
+++ b/spec/gush/workflow_spec.rb
@@ -78,6 +78,40 @@ def configure(*args)
       flow = TestWorkflow.create
       expect(Gush::Workflow.page.map(&:id)).to eq([flow.id])
     end
+
+    it "does not error if a stored workflow class is no longer defined in the codebase" do
+      flow = TestWorkflow.create
+      called = false
+      allow_any_instance_of(TestWorkflow).to receive(:to_hash).and_wrap_original do |original, *args|
+        called = true
+        original.call(*args).merge({name: 'OldDeletedWorkflow', klass: 'OldDeletedWorkflow'})
+      end
+      expect {
+        flow.save
+        Gush::Workflow.page
+      }.not_to raise_error
+      expect {
+        Gush::Client.new.find_workflow(flow.id)
+      }.to raise_error(Gush::WorkflowClassDoesNotExist)
+      expect(called).to be(true)
+    end
+
+    it "does not error if a workflow's job class is no longer defined" do
+      flow = TestWorkflow.create
+      called = false
+      allow_any_instance_of(Gush::Job).to receive(:as_json).and_wrap_original do |original, *args|
+        called = true
+        original.call(*args).merge({ klass: 'OldDeletedJob'})
+      end
+      flow.save
+      expect {
+        Gush::Workflow.page
+      }.not_to raise_error
+      expect {
+        Gush::Client.new.find_workflow(flow.id)
+      }.to raise_error(Gush::JobClassDoesNotExist)
+      expect(called).to be(true)
+    end
   end
 
   describe "#save" do