diff --git a/clang/include/clang/AST/Type.h b/clang/include/clang/AST/Type.h
--- a/clang/include/clang/AST/Type.h
+++ b/clang/include/clang/AST/Type.h
@@ -3953,7 +3953,7 @@
     /// The number of types in the exception specification.
     /// A whole unsigned is not needed here and according to
     /// [implimits] 8 bits would be enough here.
-    unsigned NumExceptionType = 0;
+    uint16_t NumExceptionType = 0;
   };
 
 protected:
diff --git a/clang/lib/AST/Type.cpp b/clang/lib/AST/Type.cpp
--- a/clang/lib/AST/Type.cpp
+++ b/clang/lib/AST/Type.cpp
@@ -3371,7 +3371,10 @@
   // Fill in the exception type array if present.
   if (getExceptionSpecType() == EST_Dynamic) {
     auto &ExtraBits = *getTrailingObjects<FunctionTypeExtraBitfields>();
-    ExtraBits.NumExceptionType = epi.ExceptionSpec.Exceptions.size();
+    size_t NumExceptions = epi.ExceptionSpec.Exceptions.size();
+    assert(NumExceptions <= UINT16_MAX &&
+           "Not enough bits to encode exceptions");
+    ExtraBits.NumExceptionType = NumExceptions;
 
     assert(hasExtraBitfields() && "missing trailing extra bitfields!");
     auto *exnSlot =