diff --git a/services/document-updater/app/coffee/UpdateManager.coffee b/services/document-updater/app/coffee/UpdateManager.coffee
index e5ede11173..3d0a318b9b 100644
--- a/services/document-updater/app/coffee/UpdateManager.coffee
+++ b/services/document-updater/app/coffee/UpdateManager.coffee
@@ -138,10 +138,13 @@ module.exports = UpdateManager =
 		# 16-bit character of a blackboard bold character (http://www.fileformat.info/info/unicode/char/1d400/index.htm).
 		# Something must be going on client side that is screwing up the encoding and splitting the
 		# two 16-bit characters so that \uD835 is standalone.
+		BAD_CHAR_REGEXP = /[\uD800-\uDFFF]/g
 		for op in update.op or []
-			if op.i?
+			if op.i? && BAD_CHAR_REGEXP.test(op.i)
 				# Replace high and low surrogate characters with 'replacement character' (\uFFFD)
-				op.i = op.i.replace(/[\uD800-\uDFFF]/g, "\uFFFD")
+				op.i = op.i.replace(BAD_CHAR_REGEXP, "\uFFFD")
+				# remove any client-side hash because we have modified the content
+				delete update.hash
 		return update
 
 	_addProjectHistoryMetadataToOps: (updates, pathname, projectHistoryId, lines) ->
diff --git a/services/document-updater/test/unit/coffee/UpdateManager/UpdateManagerTests.coffee b/services/document-updater/test/unit/coffee/UpdateManager/UpdateManagerTests.coffee
index ac8d4c742c..280fad5f33 100644
--- a/services/document-updater/test/unit/coffee/UpdateManager/UpdateManagerTests.coffee
+++ b/services/document-updater/test/unit/coffee/UpdateManager/UpdateManagerTests.coffee
@@ -212,7 +212,7 @@ describe "UpdateManager", ->
 
 		describe "with UTF-16 surrogate pairs in the update", ->
 			beforeEach ->
-				@update = {op: [{p: 42, i: "\uD835\uDC00"}]}
+				@update = {op: [{p: 42, i: "\uD835\uDC00"}], hash: "f1d2d2f924e986ac86fdf7b36c94bcdf32beec15"}
 				@UpdateManager.applyUpdate @project_id, @doc_id, @update, @callback
 
 			it "should apply the update but with surrogate pairs removed", ->
@@ -223,6 +223,9 @@ describe "UpdateManager", ->
 				# \uFFFD is 'replacement character'
 				@update.op[0].i.should.equal "\uFFFD\uFFFD"
 
+			it "should skip the hash check by removing any hash field present", ->
+				@update.should.not.have.property('hash')
+
 		describe "with an error", ->
 			beforeEach ->
 				@error = new Error("something went wrong")