diff --git a/src/vs/monaco.d.ts b/src/vs/monaco.d.ts
index 9165cba0dc64db7f3b70e915d5cf6974d6783822..6396279982ec503190943bfdd3c564c4a4771ed9 100644
--- a/src/vs/monaco.d.ts
+++ b/src/vs/monaco.d.ts
@@ -1546,7 +1546,7 @@ declare module monaco.editor {
 		 * @param limitResultCount Limit the number of results
 		 * @return The ranges where the matches are. It is empty if not matches have been found.
 		 */
-		findMatches(searchString: string, searchOnlyEditableRange: boolean, isRegex: boolean, matchCase: boolean, wordSeparators: string, captureMatches: boolean, limitResultCount?: number): FindMatch[];
+		findMatches(searchString: string, searchOnlyEditableRange: boolean, isRegex: boolean, matchCase: boolean, wordSeparators: string | null, captureMatches: boolean, limitResultCount?: number): FindMatch[];
 		/**
 		 * Search the model.
 		 * @param searchString The string used to search. If it is a regular expression, set `isRegex` to true.
@@ -1558,7 +1558,7 @@ declare module monaco.editor {
 		 * @param limitResultCount Limit the number of results
 		 * @return The ranges where the matches are. It is empty if no matches have been found.
 		 */
-		findMatches(searchString: string, searchScope: IRange, isRegex: boolean, matchCase: boolean, wordSeparators: string, captureMatches: boolean, limitResultCount?: number): FindMatch[];
+		findMatches(searchString: string, searchScope: IRange, isRegex: boolean, matchCase: boolean, wordSeparators: string | null, captureMatches: boolean, limitResultCount?: number): FindMatch[];
 		/**
 		 * Search the model for the next match. Loops to the beginning of the model if needed.
 		 * @param searchString The string used to search. If it is a regular expression, set `isRegex` to true.
@@ -1569,7 +1569,7 @@ declare module monaco.editor {
 		 * @param captureMatches The result will contain the captured groups.
 		 * @return The range where the next match is. It is null if no next match has been found.
 		 */
-		findNextMatch(searchString: string, searchStart: IPosition, isRegex: boolean, matchCase: boolean, wordSeparators: string, captureMatches: boolean): FindMatch;
+		findNextMatch(searchString: string, searchStart: IPosition, isRegex: boolean, matchCase: boolean, wordSeparators: string | null, captureMatches: boolean): FindMatch;
 		/**
 		 * Search the model for the previous match. Loops to the end of the model if needed.
 		 * @param searchString The string used to search. If it is a regular expression, set `isRegex` to true.
@@ -1580,7 +1580,7 @@ declare module monaco.editor {
 		 * @param captureMatches The result will contain the captured groups.
 		 * @return The range where the previous match is. It is null if no previous match has been found.
 		 */
-		findPreviousMatch(searchString: string, searchStart: IPosition, isRegex: boolean, matchCase: boolean, wordSeparators: string, captureMatches: boolean): FindMatch;
+		findPreviousMatch(searchString: string, searchStart: IPosition, isRegex: boolean, matchCase: boolean, wordSeparators: string | null, captureMatches: boolean): FindMatch;
 		/**
 		 * Get the language associated with this model.
 		 */