Index: plugins/clang/clangsupport.cpp
===================================================================
--- plugins/clang/clangsupport.cpp
+++ plugins/clang/clangsupport.cpp
@@ -180,12 +180,13 @@
     clangDebug() << "Detected Clang version:" << ClangHelpers::clangVersion();
 
     {
-        const auto builtinDir = ClangHelpers::clangBuiltinIncludePath();
         const auto headerToCheck = QLatin1String("cpuid.h");
-        if (!QFile::exists(builtinDir + QLatin1Char('/') + headerToCheck)) {
+        const auto builtinDir = ClangHelpers::clangBuiltinIncludePath(headerToCheck);
+        if (builtinDir.isEmpty()) {
             setErrorDescription(i18n("The clang builtin include path \"%1\" is invalid (missing %2 header).\n"
                                      "Try setting the KDEV_CLANG_BUILTIN_DIR environment variable manually to fix this.\n"
-                                     "See also: https://bugs.kde.org/show_bug.cgi?id=393779", builtinDir, headerToCheck));
+                                     "See also: https://bugs.kde.org/show_bug.cgi?id=393779",
+                                     ClangHelpers::clangBuiltinIncludePath(), headerToCheck));
             return;
         }
     }
Index: plugins/clang/duchain/clanghelpers.h
===================================================================
--- plugins/clang/duchain/clanghelpers.h
+++ plugins/clang/duchain/clanghelpers.h
@@ -104,10 +104,15 @@
 
 /**
  * @return The path containing Clang built includes (e.g. stddef.h, stdarg.h, cpuid.h)
+ * The returned path is the env. var KDEV_CLANG_BUILTIN_DIR when set otherwise the path
+ * to the headers used when kdev-clang was built, possibly updated for minor upgrades to
+ * the library (e.g. 7.0.0 -> 7.0.1).
+ * Returns an empty string if none of the checked locations contain the file @a entryToCheck
+ * (the default entry '.' is present in any directory).
  *
  * Also see: https://clang.llvm.org/docs/FAQ.html
  */
-KDEVCLANGPRIVATE_EXPORT QString clangBuiltinIncludePath();
+KDEVCLANGPRIVATE_EXPORT QString clangBuiltinIncludePath(const QString entryToCheck=QStringLiteral("."));
 
 }
 
Index: plugins/clang/duchain/clanghelpers.cpp
===================================================================
--- plugins/clang/duchain/clanghelpers.cpp
+++ plugins/clang/duchain/clanghelpers.cpp
@@ -369,11 +369,11 @@
     return clangVersion;
 }
 
-QString ClangHelpers::clangBuiltinIncludePath()
+QString ClangHelpers::clangBuiltinIncludePath(const QString entryToCheck)
 {
-    static const auto dir = []() -> QString {
+    static const auto dir = [entryToCheck]() -> QString {
         auto dir = QString::fromUtf8(qgetenv("KDEV_CLANG_BUILTIN_DIR"));
-        if (!dir.isEmpty()) {
+        if (!dir.isEmpty() && QFile::exists(dir + QLatin1Char('/') + entryToCheck)) {
             clangDebug() << "Using dir from $KDEV_CLANG_BUILTIN_DIR:" << dir;
             return dir;
         }
@@ -383,13 +383,31 @@
         dir = QDir::cleanPath(QStringLiteral("%1/../lib/clang/%2/include")
             .arg(QCoreApplication::applicationDirPath(), clangVersion()));
         clangDebug() << "Trying" << dir;
-        if (QFileInfo(dir).isDir()) {
+        if (QFileInfo(dir).isDir()
+            && QFile::exists(dir + QLatin1Char('/') + entryToCheck)) {
             return dir;
         }
+#elif defined(Q_OS_UNIX)
+        // a clang minor version upgrade since we were last built can
+        // cause problems if the "clang/$fullversion/include" path component
+        // changed. Try to generate the correct builtin_dir for the current
+        // major.minor.patchlevel version: pop the last 2 components then
+        // chdir through with the updated version directory.
+        auto hardcodedDir = QDir(QStringLiteral(KDEV_CLANG_BUILTIN_DIR));
+        if (hardcodedDir.cd(QStringLiteral("../../%1/include").arg(clangVersion()))
+            && QFile::exists(hardcodedDir.path() + QLatin1Char('/') + entryToCheck)) {
+            clangDebug() << "Using builtin dir:" << hardcodedDir.path();
+            return hardcodedDir.path();
+        }
 #endif
 
-        clangDebug() << "Using builtin dir:" << KDEV_CLANG_BUILTIN_DIR;
-        return QString::fromUtf8(KDEV_CLANG_BUILTIN_DIR);
+        dir = QString::fromUtf8(KDEV_CLANG_BUILTIN_DIR);
+        if (QFile::exists(dir + QLatin1Char('/') + entryToCheck)) {
+            clangDebug() << "Using builtin dir:" << KDEV_CLANG_BUILTIN_DIR;
+            return dir;
+        }
+        // return empty string to signal failure
+        return QString();
     }();
     return dir;
 }
Index: plugins/clang/duchain/parsesession.cpp
===================================================================
--- plugins/clang/duchain/parsesession.cpp
+++ plugins/clang/duchain/parsesession.cpp
@@ -273,8 +273,12 @@
     addFrameworkDirectories(&clangArguments, &smartArgs, frameworkDirectories.project, "-F");
 
     // libclang cannot find it's builtin dir automatically, we have to specify it manually
-    smartArgs << ClangHelpers::clangBuiltinIncludePath().toUtf8();
-    clangArguments << "-isystem" << smartArgs.last().constData();
+    const auto builtinDir = ClangHelpers::clangBuiltinIncludePath();
+    // builtinDir should never be empty, still, let's not add a stray -isystem to the argument list.
+    if (!builtinDir.isEmpty()) {
+        smartArgs << builtinDir.toUtf8();
+        clangArguments << "-isystem" << smartArgs.last().constData();
+    }
 
     smartArgs << writeDefinesFile(environment.defines());
     clangArguments << "-imacros" << smartArgs.last().constData();