diff --git a/clang-tools-extra/clangd/TUScheduler.cpp b/clang-tools-extra/clangd/TUScheduler.cpp
--- a/clang-tools-extra/clangd/TUScheduler.cpp
+++ b/clang-tools-extra/clangd/TUScheduler.cpp
@@ -948,7 +948,8 @@
     // rebuild. Newly built preamble cannot emit diagnostics before this call
     // finishes (ast callbacks are called from astpeer thread), hence we
     // gurantee eventual consistency.
-    if (LatestPreamble && Config::current().Diagnostics.AllowStalePreamble)
+    if (LatestPreamble && WantDiags != WantDiagnostics::No &&
+        Config::current().Diagnostics.AllowStalePreamble)
       generateDiagnostics(std::move(Invocation), std::move(Inputs),
                           std::move(CompilerInvocationDiags));
 
diff --git a/clang-tools-extra/clangd/unittests/TUSchedulerTests.cpp b/clang-tools-extra/clangd/unittests/TUSchedulerTests.cpp
--- a/clang-tools-extra/clangd/unittests/TUSchedulerTests.cpp
+++ b/clang-tools-extra/clangd/unittests/TUSchedulerTests.cpp
@@ -1309,6 +1309,13 @@
 
   // Make sure that we have eventual consistency.
   EXPECT_THAT(Collector.diagVersions().back(), Pair(PI.Version, PI.Version));
+
+  // Check that WantDiagnostics::No doesn't emit any diags.
+  PI.Version = "4";
+  PI.Contents = "#define FOO\n" + PI.Version;
+  S.update(File, PI, WantDiagnostics::No);
+  S.blockUntilIdle(timeoutSeconds(5));
+  EXPECT_THAT(Collector.diagVersions().back(), Pair("3", "3"));
 }
 
 // If a header file is missing from the CDB (or inferred using heuristics), and