diff --git a/state/remote/atlas.go b/state/remote/atlas.go
index 9a93730f3..f33f407ce 100644
--- a/state/remote/atlas.go
+++ b/state/remote/atlas.go
@@ -6,6 +6,7 @@ import (
 	"encoding/base64"
 	"fmt"
 	"io"
+	"log"
 	"net/http"
 	"net/url"
 	"os"
@@ -13,6 +14,7 @@ import (
 	"strings"
 
 	"github.com/hashicorp/go-cleanhttp"
+	"github.com/hashicorp/terraform/terraform"
 )
 
 const (
@@ -75,6 +77,9 @@ type AtlasClient struct {
 	Name        string
 	AccessToken string
 	RunId       string
+	HTTPClient  *http.Client
+
+	conflictHandlingAttempted bool
 }
 
 func (c *AtlasClient) Get() (*Payload, error) {
@@ -85,7 +90,7 @@ func (c *AtlasClient) Get() (*Payload, error) {
 	}
 
 	// Request the url
-	client := cleanhttp.DefaultClient()
+	client := c.http()
 	resp, err := client.Do(req)
 	if err != nil {
 		return nil, err
@@ -164,7 +169,7 @@ func (c *AtlasClient) Put(state []byte) error {
 	req.ContentLength = int64(len(state))
 
 	// Make the request
-	client := cleanhttp.DefaultClient()
+	client := c.http()
 	resp, err := client.Do(req)
 	if err != nil {
 		return fmt.Errorf("Failed to upload state: %v", err)
@@ -175,6 +180,8 @@ func (c *AtlasClient) Put(state []byte) error {
 	switch resp.StatusCode {
 	case http.StatusOK:
 		return nil
+	case http.StatusConflict:
+		return c.handleConflict(c.readBody(resp.Body), state)
 	default:
 		return fmt.Errorf(
 			"HTTP error: %d\n\nBody: %s",
@@ -190,7 +197,7 @@ func (c *AtlasClient) Delete() error {
 	}
 
 	// Make the request
-	client := cleanhttp.DefaultClient()
+	client := c.http()
 	resp, err := client.Do(req)
 	if err != nil {
 		return fmt.Errorf("Failed to delete state: %v", err)
@@ -241,3 +248,74 @@ func (c *AtlasClient) url() *url.URL {
 		RawQuery: values.Encode(),
 	}
 }
+
+func (c *AtlasClient) http() *http.Client {
+	if c.HTTPClient != nil {
+		return c.HTTPClient
+	}
+	return cleanhttp.DefaultClient()
+}
+
+// Atlas returns an HTTP 409 - Conflict if the pushed state reports the same
+// Serial number but the checksum of the raw content differs. This can
+// sometimes happen when Terraform changes state representation internally
+// between versions in a way that's semantically neutral but affects the JSON
+// output and therefore the checksum.
+//
+// Here we detect and handle this situation by ticking the serial and retrying
+// iff for the previous state and the proposed state:
+//
+//   * the serials match
+//   * the parsed states are Equal (semantically equivalent)
+//
+// In other words, in this situation Terraform can override Atlas's detected
+// conflict by asserting that the state it is pushing is indeed correct.
+func (c *AtlasClient) handleConflict(msg string, state []byte) error {
+	log.Printf("[DEBUG] Handling Atlas conflict response: %s", msg)
+
+	if c.conflictHandlingAttempted {
+		log.Printf("[DEBUG] Already attempted conflict resolution; returning conflict.")
+	} else {
+		c.conflictHandlingAttempted = true
+		log.Printf("[DEBUG] Atlas reported conflict, checking for equivalent states.")
+
+		payload, err := c.Get()
+		if err != nil {
+			return conflictHandlingError(err)
+		}
+
+		currentState, err := terraform.ReadState(bytes.NewReader(payload.Data))
+		if err != nil {
+			return conflictHandlingError(err)
+		}
+
+		proposedState, err := terraform.ReadState(bytes.NewReader(state))
+		if err != nil {
+			return conflictHandlingError(err)
+		}
+
+		if statesAreEquivalent(currentState, proposedState) {
+			log.Printf("[DEBUG] States are equivalent, incrementing serial and retrying.")
+			proposedState.Serial++
+			var buf bytes.Buffer
+			if err := terraform.WriteState(proposedState, &buf); err != nil {
+				return conflictHandlingError(err)
+			}
+			return c.Put(buf.Bytes())
+		} else {
+			log.Printf("[DEBUG] States are not equivalent, returning conflict.")
+		}
+	}
+
+	return fmt.Errorf(
+		"Atlas detected a remote state conflict.\n\nMessage: %s", msg)
+}
+
+func conflictHandlingError(err error) error {
+	return fmt.Errorf(
+		"Error while handling a conflict response from Atlas: %s", err)
+}
+
+func statesAreEquivalent(current, proposed *terraform.State) bool {
+	return current.Serial == proposed.Serial && current.Equal(proposed)
+}
diff --git a/state/remote/atlas_test.go b/state/remote/atlas_test.go
index 202e15dad..ae7ee8a1b 100644
--- a/state/remote/atlas_test.go
+++ b/state/remote/atlas_test.go
@@ -1,9 +1,15 @@
 package remote
 
 import (
+	"bytes"
+	"crypto/md5"
 	"net/http"
+	"net/http/httptest"
 	"os"
 	"testing"
+	"time"
+
+	"github.com/hashicorp/terraform/terraform"
 )
 
 func TestAtlasClient_impl(t *testing.T) {
@@ -30,3 +36,259 @@ func TestAtlasClient(t *testing.T) {
 
 	testClient(t, client)
 }
+
+func TestAtlasClient_ReportedConflictEqualStates(t *testing.T) {
+	fakeAtlas := newFakeAtlas(t, testStateModuleOrderChange)
+	srv := fakeAtlas.Server()
+	defer srv.Close()
+	client, err := atlasFactory(map[string]string{
+		"access_token": "sometoken",
+		"name":         "someuser/some-test-remote-state",
+		"address":      srv.URL,
+	})
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	state, err := terraform.ReadState(bytes.NewReader(testStateModuleOrderChange))
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	var stateJson bytes.Buffer
+	if err := terraform.WriteState(state, &stateJson); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	if err := client.Put(stateJson.Bytes()); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+}
+
+func TestAtlasClient_NoConflict(t *testing.T) {
+	fakeAtlas := newFakeAtlas(t, testStateSimple)
+	srv := fakeAtlas.Server()
+	defer srv.Close()
+	client, err := atlasFactory(map[string]string{
+		"access_token": "sometoken",
+		"name":         "someuser/some-test-remote-state",
+		"address":      srv.URL,
+	})
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	state, err := terraform.ReadState(bytes.NewReader(testStateSimple))
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	fakeAtlas.NoConflictAllowed(true)
+
+	var stateJson bytes.Buffer
+	if err := terraform.WriteState(state, &stateJson); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	if err := client.Put(stateJson.Bytes()); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+}
+
+func TestAtlasClient_LegitimateConflict(t *testing.T) {
+	fakeAtlas := newFakeAtlas(t, testStateSimple)
+	srv := fakeAtlas.Server()
+	defer srv.Close()
+	client, err := atlasFactory(map[string]string{
+		"access_token": "sometoken",
+		"name":         "someuser/some-test-remote-state",
+		"address":      srv.URL,
+	})
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	state, err := terraform.ReadState(bytes.NewReader(testStateSimple))
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	// Changing the state but not the serial. Should generate a conflict.
+	state.RootModule().Outputs["drift"] = "happens"
+
+	var stateJson bytes.Buffer
+	if err := terraform.WriteState(state, &stateJson); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	if err := client.Put(stateJson.Bytes()); err == nil {
+		t.Fatal("Expected error from state conflict, got none.")
+	}
+}
+
+func TestAtlasClient_UnresolvableConflict(t *testing.T) {
+	fakeAtlas := newFakeAtlas(t, testStateSimple)
+
+	// Something unexpected causes Atlas to conflict in a way that we can't fix.
+	fakeAtlas.AlwaysConflict(true)
+
+	srv := fakeAtlas.Server()
+	defer srv.Close()
+	client, err := atlasFactory(map[string]string{
+		"access_token": "sometoken",
+		"name":         "someuser/some-test-remote-state",
+		"address":      srv.URL,
+	})
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	state, err := terraform.ReadState(bytes.NewReader(testStateSimple))
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	var stateJson bytes.Buffer
+	if err := terraform.WriteState(state, &stateJson); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	doneCh := make(chan struct{})
+	go func() {
+		defer close(doneCh)
+		if err := client.Put(stateJson.Bytes()); err == nil {
+			t.Fatal("Expected error from state conflict, got none.")
+		}
+	}()
+
+	select {
+	case <-doneCh:
+		// OK
+	case <-time.After(50 * time.Millisecond):
+		t.Fatalf("Timed out after 50ms, probably because retrying infinitely.")
+	}
+}
+
+// Stub Atlas HTTP API for a given state JSON string; does checksum-based
+// conflict detection equivalent to Atlas's.
+type fakeAtlas struct {
+	state []byte
+	t     *testing.T
+
+	// Used to test that we only do the special conflict handling retry once.
+	alwaysConflict bool
+
+	// Used to fail the test immediately if a conflict happens.
+	noConflictAllowed bool
+}
+
+func newFakeAtlas(t *testing.T, state []byte) *fakeAtlas {
+	return &fakeAtlas{
+		state: state,
+		t:     t,
+	}
+}
+
+func (f *fakeAtlas) Server() *httptest.Server {
+	return httptest.NewServer(http.HandlerFunc(f.handler))
+}
+
+func (f *fakeAtlas) CurrentState() *terraform.State {
+	currentState, err := terraform.ReadState(bytes.NewReader(f.state))
+	if err != nil {
+		f.t.Fatalf("err: %s", err)
+	}
+	return currentState
+}
+
+func (f *fakeAtlas) CurrentSerial() int64 {
+	return f.CurrentState().Serial
+}
+
+func (f *fakeAtlas) CurrentSum() [md5.Size]byte {
+	return md5.Sum(f.state)
+}
+
+func (f *fakeAtlas) AlwaysConflict(b bool) {
+	f.alwaysConflict = b
+}
+
+func (f *fakeAtlas) NoConflictAllowed(b bool) {
+	f.noConflictAllowed = b
+}
+
+func (f *fakeAtlas) handler(resp http.ResponseWriter, req *http.Request) {
+	switch req.Method {
+	case "GET":
+		// Respond with the current stored state.
+		resp.Header().Set("Content-Type", "application/json")
+		resp.Write(f.state)
+	case "PUT":
+		var buf bytes.Buffer
+		buf.ReadFrom(req.Body)
+		sum := md5.Sum(buf.Bytes())
+		state, err := terraform.ReadState(&buf)
+		if err != nil {
+			f.t.Fatalf("err: %s", err)
+		}
+		conflict := f.CurrentSerial() == state.Serial && f.CurrentSum() != sum
+		conflict = conflict || f.alwaysConflict
+		if conflict {
+			if f.noConflictAllowed {
+				f.t.Fatal("Got conflict when NoConflictAllowed was set.")
+			}
+			http.Error(resp, "Conflict", 409)
+		} else {
+			f.state = buf.Bytes()
+			resp.WriteHeader(200)
+		}
+	}
+}
+
+// This is a tfstate file with the module order changed, which is a structural
+// but not a semantic difference. Terraform will sort these modules as it
+// loads the state.
+var testStateModuleOrderChange = []byte(
+	`{
+    "version": 1,
+    "serial": 1,
+    "modules": [
+        {
+            "path": [
+                "root",
+                "child2",
+                "grandchild"
+            ],
+            "outputs": {
+                "foo": "bar2"
+            },
+            "resources": null
+        },
+        {
+            "path": [
+                "root",
+                "child1",
+                "grandchild"
+            ],
+            "outputs": {
+                "foo": "bar1"
+            },
+            "resources": null
+        }
+    ]
+}
+`)
+
+var testStateSimple = []byte(
+	`{
+    "version": 1,
+    "serial": 1,
+    "modules": [
+        {
+            "path": [
+                "root"
+            ],
+            "outputs": {
+                "foo": "bar"
+            },
+            "resources": null
+        }
+    ]
+}
+`)