diff --git a/clang/lib/Lex/DependencyDirectivesSourceMinimizer.cpp b/clang/lib/Lex/DependencyDirectivesSourceMinimizer.cpp
--- a/clang/lib/Lex/DependencyDirectivesSourceMinimizer.cpp
+++ b/clang/lib/Lex/DependencyDirectivesSourceMinimizer.cpp
@@ -270,6 +270,15 @@
   return Last;
 }
 
+static const char *findLastNonSpaceNonBackslash(const char *First,
+                                                const char *Last) {
+  assert(First <= Last);
+  while (First != Last &&
+         (isHorizontalWhitespace(Last[-1]) || Last[-1] == '\\'))
+    --Last;
+  return Last;
+}
+
 static const char *findFirstTrailingSpace(const char *First,
                                           const char *Last) {
   const char *LastNonSpace = findLastNonSpace(First, Last);
@@ -434,11 +443,11 @@
       return;
     }
 
-    // Print up to the backslash, backing up over spaces. Preserve at least one
-    // space, as the space matters when tokens are separated by a line
-    // continuation.
-    append(First, findFirstTrailingSpace(
-                      First, LastBeforeTrailingSpace - 1));
+    // Print up to the last character that's not a whitespace or backslash.
+    // Then print exactly one space, which matters when tokens are separated by
+    // a line continuation.
+    append(First, findLastNonSpaceNonBackslash(First, Last));
+    put(' ');
 
     First = Last;
     skipNewline(First, End);
diff --git a/clang/unittests/Lex/DependencyDirectivesSourceMinimizerTest.cpp b/clang/unittests/Lex/DependencyDirectivesSourceMinimizerTest.cpp
--- a/clang/unittests/Lex/DependencyDirectivesSourceMinimizerTest.cpp
+++ b/clang/unittests/Lex/DependencyDirectivesSourceMinimizerTest.cpp
@@ -713,6 +713,17 @@
       Out.data());
 }
 
+TEST(MinimizeSourceToDependencyDirectivesTest,
+     SupportWhitespaceBeforeLineContinuation) {
+  SmallVector<char, 128> Out;
+
+  ASSERT_FALSE(minimizeSourceToDependencyDirectives("#define FOO(BAR) \\\n"
+                                                    "  #BAR\\\n"
+                                                    "  baz\n",
+                                                    Out));
+  EXPECT_STREQ("#define FOO(BAR) #BAR baz\n", Out.data());
+}
+
 TEST(MinimizeSourceToDependencyDirectivesTest,
      SupportWhitespaceBeforeLineContinuationInStringSkipping) {
   SmallVector<char, 128> Out;