diff --git a/clang-tools-extra/clangd/Diagnostics.cpp b/clang-tools-extra/clangd/Diagnostics.cpp
--- a/clang-tools-extra/clangd/Diagnostics.cpp
+++ b/clang-tools-extra/clangd/Diagnostics.cpp
@@ -31,6 +31,7 @@
 #include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
+#include <cassert>
 #include <cstddef>
 #include <vector>
 
@@ -463,7 +464,8 @@
 
   // Main diagnostic should always refer to a range inside main file. If a
   // diagnostic made it so for, it means either itself or one of its notes is
-  // inside main file.
+  // inside main file. It's also possible that there's a fix in the main file,
+  // but we preserve fixes iff primary diagnostic is in the main file.
   if (D.InsideMainFile) {
     Main.range = D.Range;
   } else {
@@ -701,13 +703,12 @@
     return;
   }
 
-  bool InsideMainFile = isInsideMainFile(Info);
   SourceManager &SM = Info.getSourceManager();
 
   auto FillDiagBase = [&](DiagBase &D) {
     fillNonLocationData(DiagLevel, Info, D);
 
-    D.InsideMainFile = InsideMainFile;
+    D.InsideMainFile = isInsideMainFile(Info);
     D.Range = diagnosticRange(Info, *LangOpts);
     D.File = std::string(SM.getFilename(Info.getLocation()));
     D.AbsFile = getCanonicalPath(
@@ -719,9 +720,9 @@
   auto AddFix = [&](bool SyntheticMessage) -> bool {
     assert(!Info.getFixItHints().empty() &&
            "diagnostic does not have attached fix-its");
-    if (!InsideMainFile)
+    // No point in generating fixes, if the diagnostic is for a different file.
+    if (!LastDiag->InsideMainFile)
       return false;
-
     // Copy as we may modify the ranges.
     auto FixIts = Info.getFixItHints().vec();
     llvm::SmallVector<TextEdit, 1> Edits;
diff --git a/clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp b/clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp
--- a/clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp
+++ b/clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp
@@ -22,6 +22,7 @@
 #include "support/Path.h"
 #include "clang/Basic/Diagnostic.h"
 #include "clang/Basic/DiagnosticSema.h"
+#include "llvm/ADT/StringRef.h"
 #include "llvm/Support/ScopedPrinter.h"
 #include "llvm/Support/TargetSelect.h"
 #include "gmock/gmock.h"
@@ -1680,6 +1681,28 @@
   EXPECT_THAT(*TU.build().getDiagnostics(), IsEmpty());
 }
 
+TEST(DiagnosticsTest, FixItFromHeader) {
+  llvm::StringLiteral Header(R"cpp(
+    void foo(int *);
+    void foo(int *, int);)cpp");
+  Annotations Source(R"cpp(
+  /*error-ok*/
+    void bar() {
+      int x;
+      $diag[[foo]]($fix[[]]x, 1);
+    })cpp");
+  TestTU TU;
+  TU.Code = Source.code().str();
+  TU.HeaderCode = Header.str();
+  EXPECT_THAT(
+      *TU.build().getDiagnostics(),
+      UnorderedElementsAre(AllOf(
+          Diag(Source.range("diag"), "no matching function for call to 'foo'"),
+          withFix(Fix(Source.range("fix"), "&",
+                      "candidate function not viable: no known conversion from "
+                      "'int' to 'int *' for 1st argument; take the address of "
+                      "the argument with &")))));
+}
 } // namespace
 } // namespace clangd
 } // namespace clang