diff --git a/clang-tools-extra/clangd/index/CanonicalIncludes.cpp b/clang-tools-extra/clangd/index/CanonicalIncludes.cpp
--- a/clang-tools-extra/clangd/index/CanonicalIncludes.cpp
+++ b/clang-tools-extra/clangd/index/CanonicalIncludes.cpp
@@ -772,7 +772,10 @@
                   MaxSuffixComponents;
          }) != SystemHeaderMap->keys().end());
 
-  StdSuffixHeaderMapping = SystemHeaderMap;
+  // FIXME: Suffix mapping contains invalid entries for C, so only enable it for
+  // CPP.
+  if (Language.CPlusPlus)
+    StdSuffixHeaderMapping = SystemHeaderMap;
 }
 
 } // namespace clangd
diff --git a/clang-tools-extra/clangd/unittests/CanonicalIncludesTests.cpp b/clang-tools-extra/clangd/unittests/CanonicalIncludesTests.cpp
--- a/clang-tools-extra/clangd/unittests/CanonicalIncludesTests.cpp
+++ b/clang-tools-extra/clangd/unittests/CanonicalIncludesTests.cpp
@@ -21,6 +21,10 @@
   CI.addSystemHeadersMapping(Language);
   // Usual standard library symbols are mapped correctly.
   EXPECT_EQ("<stdio.h>", CI.mapHeader("path/stdio.h", "printf"));
+  // Suffix mapping isn't available for C, instead of mapping to `<cstdio> we
+  // just leave the header as-is.
+  EXPECT_EQ("include/stdio.h",
+            CI.mapHeader("include/stdio.h", "unknown_symbol"));
 }
 
 TEST(CanonicalIncludesTest, CXXStandardLibrary) {