diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
--- a/clang/lib/Format/TokenAnnotator.cpp
+++ b/clang/lib/Format/TokenAnnotator.cpp
@@ -3080,7 +3080,8 @@
 
     // space between keywords and paren e.g. "using ("
     if (Right.is(tok::l_paren))
-      if (Left.isOneOf(tok::kw_using, Keywords.kw_async, Keywords.kw_when))
+      if (Left.isOneOf(tok::kw_using, Keywords.kw_async, Keywords.kw_when,
+                       Keywords.kw_lock))
         return Style.SpaceBeforeParens == FormatStyle::SBPO_ControlStatements ||
                spaceRequiredBeforeParens(Right);
   } else if (Style.Language == FormatStyle::LK_JavaScript) {
diff --git a/clang/unittests/Format/FormatTestCSharp.cpp b/clang/unittests/Format/FormatTestCSharp.cpp
--- a/clang/unittests/Format/FormatTestCSharp.cpp
+++ b/clang/unittests/Format/FormatTestCSharp.cpp
@@ -741,6 +741,9 @@
 })",
                Style);
 
+  // space after lock in `lock (processes)`.
+  verifyFormat("lock (process)", Style);
+
   Style.SpacesInSquareBrackets = true;
   verifyFormat(R"(private float[ , ] Values;)", Style);
   verifyFormat(R"(string dirPath = args?[ 0 ];)", Style);