diff --git a/certificate_checker.cc b/certificate_checker.cc
index 7432c21..75bd6be 100644
--- a/certificate_checker.cc
+++ b/certificate_checker.cc
@@ -15,6 +15,7 @@
 #include <openssl/evp.h>
 #include <openssl/ssl.h>
 
+#include "update_engine/constants.h"
 #include "update_engine/prefs_interface.h"
 #include "update_engine/utils.h"
 
diff --git a/certificate_checker_unittest.cc b/certificate_checker_unittest.cc
index 4b33e02..eb7067f 100644
--- a/certificate_checker_unittest.cc
+++ b/certificate_checker_unittest.cc
@@ -12,6 +12,7 @@
 
 #include "update_engine/certificate_checker.h"
 #include "update_engine/certificate_checker_mock.h"
+#include "update_engine/constants.h"
 #include "update_engine/mock_system_state.h"
 #include "update_engine/prefs_mock.h"
 
diff --git a/constants.cc b/constants.cc
index 4b87a58..f9c6ce5 100644
--- a/constants.cc
+++ b/constants.cc
@@ -10,4 +10,34 @@
   "/mnt/stateful_partition/factory_install_reset";
 
 const char kPowerwashCommand[] = "safe fast\n";
+
+
+// Constants defining keys for the persisted state of update engine.
+const char kPrefsBackoffExpiryTime[] = "backoff-expiry-time";
+const char kPrefsCertificateReportToSendDownload[] =
+    "certificate-report-to-send-download";
+const char kPrefsCertificateReportToSendUpdate[] =
+    "certificate-report-to-send-update";
+const char kPrefsCurrentResponseSignature[] = "current-response-signature";
+const char kPrefsCurrentUrlFailureCount[] = "current-url-failure-count";
+const char kPrefsCurrentUrlIndex[] = "current-url-index";
+const char kPrefsDeltaUpdateFailures[] = "delta-update-failures";
+const char kPrefsLastActivePingDay[] = "last-active-ping-day";
+const char kPrefsLastRollCallPingDay[] = "last-roll-call-ping-day";
+const char kPrefsManifestMetadataSize[] = "manifest-metadata-size";
+const char kPrefsPayloadAttemptNumber[] = "payload-attempt-number";
+const char kPrefsPreviousVersion[] = "previous-version";
+const char kPrefsResumedUpdateFailures[] = "resumed-update-failures";
+const char kPrefsUpdateCheckCount[] = "update-check-count";
+const char kPrefsUpdateCheckResponseHash[] = "update-check-response-hash";
+const char kPrefsUpdateFirstSeenAt[] = "update-first-seen-at";
+const char kPrefsUpdateServerCertificate[] = "update-server-cert";
+const char kPrefsUpdateStateNextDataOffset[] = "update-state-next-data-offset";
+const char kPrefsUpdateStateNextOperation[] = "update-state-next-operation";
+const char kPrefsUpdateStateSHA256Context[] = "update-state-sha-256-context";
+const char kPrefsUpdateStateSignatureBlob[] = "update-state-signature-blob";
+const char kPrefsUpdateStateSignedSHA256Context[] =
+    "update-state-signed-sha-256-context";
+const char kPrefsWallClockWaitPeriod[] = "wall-clock-wait-period";
+
 }
diff --git a/constants.h b/constants.h
index d6fd736..5bba2d3 100644
--- a/constants.h
+++ b/constants.h
@@ -14,6 +14,31 @@
 // The contents of the powerwash marker file.
 extern const char kPowerwashCommand[];
 
+// Constants related to preferences.
+extern const char kPrefsBackoffExpiryTime[];
+extern const char kPrefsCertificateReportToSendDownload[];
+extern const char kPrefsCertificateReportToSendUpdate[];
+extern const char kPrefsCurrentResponseSignature[];
+extern const char kPrefsCurrentUrlFailureCount[];
+extern const char kPrefsCurrentUrlIndex[];
+extern const char kPrefsDeltaUpdateFailures[];
+extern const char kPrefsLastActivePingDay[];
+extern const char kPrefsLastRollCallPingDay[];
+extern const char kPrefsManifestMetadataSize[];
+extern const char kPrefsPayloadAttemptNumber[];
+extern const char kPrefsPreviousVersion[];
+extern const char kPrefsResumedUpdateFailures[];
+extern const char kPrefsUpdateCheckCount[];
+extern const char kPrefsUpdateCheckResponseHash[];
+extern const char kPrefsUpdateFirstSeenAt[];
+extern const char kPrefsUpdateServerCertificate[];
+extern const char kPrefsUpdateStateNextDataOffset[];
+extern const char kPrefsUpdateStateNextOperation[];
+extern const char kPrefsUpdateStateSHA256Context[];
+extern const char kPrefsUpdateStateSignatureBlob[];
+extern const char kPrefsUpdateStateSignedSHA256Context[];
+extern const char kPrefsWallClockWaitPeriod[];
+
 }  // namespace chromeos_update_engine
 
 #endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_CONSTANTS_H
diff --git a/delta_performer.cc b/delta_performer.cc
index 12f0e20..a815e28 100644
--- a/delta_performer.cc
+++ b/delta_performer.cc
@@ -18,6 +18,7 @@
 #include <google/protobuf/repeated_field.h>
 
 #include "update_engine/bzip_extent_writer.h"
+#include "update_engine/constants.h"
 #include "update_engine/delta_diff_generator.h"
 #include "update_engine/extent_ranges.h"
 #include "update_engine/extent_writer.h"
diff --git a/delta_performer_unittest.cc b/delta_performer_unittest.cc
index ba2e934..1c0c2b5 100644
--- a/delta_performer_unittest.cc
+++ b/delta_performer_unittest.cc
@@ -16,6 +16,7 @@
 #include <google/protobuf/repeated_field.h>
 #include <gtest/gtest.h>
 
+#include "update_engine/constants.h"
 #include "update_engine/delta_diff_generator.h"
 #include "update_engine/delta_performer.h"
 #include "update_engine/extent_ranges.h"
diff --git a/omaha_request_action.cc b/omaha_request_action.cc
index ad1f95e..043ec1d 100644
--- a/omaha_request_action.cc
+++ b/omaha_request_action.cc
@@ -19,6 +19,7 @@
 #include <libxml/xpathInternals.h>
 
 #include "update_engine/action_pipe.h"
+#include "update_engine/constants.h"
 #include "update_engine/omaha_request_params.h"
 #include "update_engine/payload_state_interface.h"
 #include "update_engine/prefs_interface.h"
diff --git a/omaha_request_action_unittest.cc b/omaha_request_action_unittest.cc
index 9bdc167..4897b7a 100644
--- a/omaha_request_action_unittest.cc
+++ b/omaha_request_action_unittest.cc
@@ -11,7 +11,9 @@
 #include <base/stringprintf.h>
 #include "base/time.h"
 #include "gtest/gtest.h"
+
 #include "update_engine/action_pipe.h"
+#include "update_engine/constants.h"
 #include "update_engine/mock_http_fetcher.h"
 #include "update_engine/omaha_hash_calculator.h"
 #include "update_engine/omaha_request_action.h"
diff --git a/omaha_response_handler_action.cc b/omaha_response_handler_action.cc
index 9c3c0db..a9f77a8 100644
--- a/omaha_response_handler_action.cc
+++ b/omaha_response_handler_action.cc
@@ -9,6 +9,7 @@
 #include <base/logging.h>
 #include "base/string_util.h"
 
+#include "update_engine/constants.h"
 #include "update_engine/delta_performer.h"
 #include "update_engine/payload_state_interface.h"
 #include "update_engine/prefs_interface.h"
diff --git a/omaha_response_handler_action_unittest.cc b/omaha_response_handler_action_unittest.cc
index 9f26bca..80dfc5c 100644
--- a/omaha_response_handler_action_unittest.cc
+++ b/omaha_response_handler_action_unittest.cc
@@ -6,6 +6,7 @@
 
 #include <gtest/gtest.h>
 
+#include "update_engine/constants.h"
 #include "update_engine/omaha_response_handler_action.h"
 #include "update_engine/mock_system_state.h"
 #include "update_engine/test_utils.h"
diff --git a/payload_state.cc b/payload_state.cc
index f5b8f36..585988a 100644
--- a/payload_state.cc
+++ b/payload_state.cc
@@ -9,7 +9,7 @@
 #include <base/logging.h>
 #include <base/stringprintf.h>
 
-#include "update_engine/prefs.h"
+#include "update_engine/constants.h"
 #include "update_engine/utils.h"
 
 using base::Time;
diff --git a/payload_state_unittest.cc b/payload_state_unittest.cc
index e647a8c..9f7f5c1 100644
--- a/payload_state_unittest.cc
+++ b/payload_state_unittest.cc
@@ -8,6 +8,7 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 
+#include "update_engine/constants.h"
 #include "update_engine/omaha_request_action.h"
 #include "update_engine/payload_state.h"
 #include "update_engine/prefs_mock.h"
diff --git a/prefs.cc b/prefs.cc
index 3af3706..496b59e 100644
--- a/prefs.cc
+++ b/prefs.cc
@@ -15,34 +15,6 @@
 
 namespace chromeos_update_engine {
 
-const char kPrefsCertificateReportToSendDownload[] =
-    "certificate-report-to-send-download";
-const char kPrefsCertificateReportToSendUpdate[] =
-    "certificate-report-to-send-update";
-const char kPrefsDeltaUpdateFailures[] = "delta-update-failures";
-const char kPrefsLastActivePingDay[] = "last-active-ping-day";
-const char kPrefsLastRollCallPingDay[] = "last-roll-call-ping-day";
-const char kPrefsManifestMetadataSize[] = "manifest-metadata-size";
-const char kPrefsPreviousVersion[] = "previous-version";
-const char kPrefsResumedUpdateFailures[] = "resumed-update-failures";
-const char kPrefsUpdateCheckResponseHash[] = "update-check-response-hash";
-const char kPrefsUpdateServerCertificate[] = "update-server-cert";
-const char kPrefsUpdateStateNextDataOffset[] = "update-state-next-data-offset";
-const char kPrefsUpdateStateNextOperation[] = "update-state-next-operation";
-const char kPrefsUpdateStateSHA256Context[] = "update-state-sha-256-context";
-const char kPrefsUpdateStateSignatureBlob[] = "update-state-signature-blob";
-const char kPrefsUpdateStateSignedSHA256Context[] =
-    "update-state-signed-sha-256-context";
-const char kPrefsUpdateCheckCount[] = "update-check-count";
-const char kPrefsWallClockWaitPeriod[] = "wall-clock-wait-period";
-const char kPrefsUpdateFirstSeenAt[] = "update-first-seen-at";
-
-const char kPrefsPayloadAttemptNumber[] = "payload-attempt-number";
-const char kPrefsCurrentResponseSignature[] = "current-response-signature";
-const char kPrefsCurrentUrlIndex[] = "current-url-index";
-const char kPrefsCurrentUrlFailureCount[] = "current-url-failure-count";
-const char kPrefsBackoffExpiryTime[] = "backoff-expiry-time";
-
 bool Prefs::Init(const FilePath& prefs_dir) {
   prefs_dir_ = prefs_dir;
   return true;
diff --git a/prefs_interface.h b/prefs_interface.h
index 14962dd..9456d52 100644
--- a/prefs_interface.h
+++ b/prefs_interface.h
@@ -9,30 +9,6 @@
 
 namespace chromeos_update_engine {
 
-extern const char kPrefsCertificateReportToSendDownload[];
-extern const char kPrefsCertificateReportToSendUpdate[];
-extern const char kPrefsDeltaUpdateFailures[];
-extern const char kPrefsLastActivePingDay[];
-extern const char kPrefsLastRollCallPingDay[];
-extern const char kPrefsManifestMetadataSize[];
-extern const char kPrefsPreviousVersion[];
-extern const char kPrefsResumedUpdateFailures[];
-extern const char kPrefsUpdateCheckResponseHash[];
-extern const char kPrefsUpdateServerCertificate[];
-extern const char kPrefsUpdateStateNextDataOffset[];
-extern const char kPrefsUpdateStateNextOperation[];
-extern const char kPrefsUpdateStateSHA256Context[];
-extern const char kPrefsUpdateStateSignatureBlob[];
-extern const char kPrefsUpdateStateSignedSHA256Context[];
-extern const char kPrefsUpdateCheckCount[];
-extern const char kPrefsWallClockWaitPeriod[];
-extern const char kPrefsUpdateFirstSeenAt[];
-extern const char kPrefsPayloadAttemptNumber[];
-extern const char kPrefsCurrentResponseSignature[];
-extern const char kPrefsCurrentUrlIndex[];
-extern const char kPrefsCurrentUrlFailureCount[];
-extern const char kPrefsBackoffExpiryTime[];
-
 // The prefs interface allows access to a persistent preferences
 // store. The two reasons for providing this as an interface are
 // testing as well as easier switching to a new implementation in the
diff --git a/prefs_mock.h b/prefs_mock.h
index 963b981..4f991fc 100644
--- a/prefs_mock.h
+++ b/prefs_mock.h
@@ -6,6 +6,7 @@
 #define CHROMEOS_PLATFORM_UPDATE_ENGINE_PREFS_MOCK_H__
 
 #include "gmock/gmock.h"
+#include "update_engine/constants.h"
 #include "update_engine/prefs_interface.h"
 
 namespace chromeos_update_engine {
diff --git a/update_attempter.cc b/update_attempter.cc
index 8ebe267..8235b19 100644
--- a/update_attempter.cc
+++ b/update_attempter.cc
@@ -22,6 +22,7 @@
 #include <policy/device_policy.h>
 
 #include "update_engine/certificate_checker.h"
+#include "update_engine/constants.h"
 #include "update_engine/dbus_service.h"
 #include "update_engine/download_action.h"
 #include "update_engine/filesystem_copier_action.h"