diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -1089,7 +1089,7 @@
   using namespace llvm::support;
 
   unsigned KeyLen = endian::readNext<uint16_t, little, unaligned>(d);
-  unsigned DataLen = endian::readNext<uint16_t, little, unaligned>(d);
+  unsigned DataLen = endian::readNext<uint32_t, little, unaligned>(d);
   return std::make_pair(KeyLen, DataLen);
 }
 
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -3599,9 +3599,7 @@
 
     // 4 bytes for each DeclID.
     unsigned DataLen = 4 * (Lookup.second - Lookup.first);
-    assert(uint16_t(DataLen) == DataLen &&
-           "too many decls for serialized lookup result");
-    LE.write<uint16_t>(DataLen);
+    LE.write<uint32_t>(DataLen);
 
     return std::make_pair(KeyLen, DataLen);
   }