diff --git a/clang-tools-extra/clangd/Preamble.cpp b/clang-tools-extra/clangd/Preamble.cpp
--- a/clang-tools-extra/clangd/Preamble.cpp
+++ b/clang-tools-extra/clangd/Preamble.cpp
@@ -8,6 +8,7 @@
 
 #include "Preamble.h"
 #include "Compiler.h"
+#include "Config.h"
 #include "Headers.h"
 #include "SourceCode.h"
 #include "support/Logger.h"
@@ -347,20 +348,24 @@
   llvm::IntrusiveRefCntPtr<DiagnosticsEngine> PreambleDiagsEngine =
       CompilerInstance::createDiagnostics(&CI.getDiagnosticOpts(),
                                           &PreambleDiagnostics, false);
-  PreambleDiagnostics.setLevelAdjuster(
-      [&](DiagnosticsEngine::Level DiagLevel, const clang::Diagnostic &Info) {
-        switch (Info.getID()) {
-        case diag::warn_no_newline_eof:
-        case diag::warn_cxx98_compat_no_newline_eof:
-        case diag::ext_no_newline_eof:
-          // If the preamble doesn't span the whole file, drop the no newline at
-          // eof warnings.
-          return Bounds.Size != ContentsBuffer->getBufferSize()
-                     ? DiagnosticsEngine::Level::Ignored
-                     : DiagLevel;
-        }
-        return DiagLevel;
-      });
+  const Config &Cfg = Config::current();
+  PreambleDiagnostics.setLevelAdjuster([&](DiagnosticsEngine::Level DiagLevel,
+                                           const clang::Diagnostic &Info) {
+    if (Cfg.Diagnostics.SuppressAll ||
+        isBuiltinDiagnosticSuppressed(Info.getID(), Cfg.Diagnostics.Suppress))
+      return DiagnosticsEngine::Ignored;
+    switch (Info.getID()) {
+    case diag::warn_no_newline_eof:
+    case diag::warn_cxx98_compat_no_newline_eof:
+    case diag::ext_no_newline_eof:
+      // If the preamble doesn't span the whole file, drop the no newline at
+      // eof warnings.
+      return Bounds.Size != ContentsBuffer->getBufferSize()
+                 ? DiagnosticsEngine::Level::Ignored
+                 : DiagLevel;
+    }
+    return DiagLevel;
+  });
 
   // Skip function bodies when building the preamble to speed up building
   // the preamble and make it smaller.
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
@@ -449,6 +449,21 @@
                                "use of undeclared identifier 'unknown'")));
 }
 
+TEST(DiagnosticTest, RespectsDiagnosticConfigInHeader) {
+  Annotations Header(R"cpp(
+    int x = "42";  // error-ok
+  )cpp");
+  Annotations Main(R"cpp(
+    #include "header.hpp"
+  )cpp");
+  auto TU = TestTU::withCode(Main.code());
+  TU.AdditionalFiles["header.hpp"] = std::string(Header.code());
+  Config Cfg;
+  Cfg.Diagnostics.Suppress.insert("init_conversion_failed");
+  WithContextValue WithCfg(Config::Key, std::move(Cfg));
+  EXPECT_THAT(*TU.build().getDiagnostics(), IsEmpty());
+}
+
 TEST(DiagnosticTest, ClangTidySuppressionComment) {
   Annotations Main(R"cpp(
     int main() {