Index: lldb/source/Target/Target.cpp
===================================================================
--- lldb/source/Target/Target.cpp
+++ lldb/source/Target/Target.cpp
@@ -2250,6 +2250,13 @@
       scratch_type_systems.emplace_back(&type_system_or_err.get());
   }
 
+  // Some TypeSystem instances are associated with several LanguageTypes so
+  // they will show up multiple times in the loop above. Filter out the
+  // duplicates as they serve no useful purpose for the caller.
+  llvm::sort(scratch_type_systems);
+  auto remove_from =
+      std::unique(scratch_type_systems.begin(), scratch_type_systems.end());
+  scratch_type_systems.erase(remove_from, scratch_type_systems.end());
   return scratch_type_systems;
 }
 
Index: lldb/test/API/lang/c/builtin-types/TestCBuiltinTypes.py
===================================================================
--- /dev/null
+++ lldb/test/API/lang/c/builtin-types/TestCBuiltinTypes.py
@@ -0,0 +1,20 @@
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+class TestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    @no_debug_info_test
+    def test_FindTypes_on_scratch_AST(self):
+        """
+        Tests FindTypes invoked with only LLDB's scratch AST present.
+        """
+        target = self.dbg.GetDummyTarget()
+        # There should be only one instance of 'unsigned long' in our single
+        # scratch AST. Note: FindTypes/SBType hahave no filter by language, so
+        # pick something that is unlikely to also be found in the scratch
+        # TypeSystem of other language plugins.
+        self.assertEqual(len(target.FindTypes("unsigned long")), 1)