diff --git a/include/swift/ABI/Metadata.h b/include/swift/ABI/Metadata.h
index 7016f8a849ab8..a619f70d81af8 100644
--- a/include/swift/ABI/Metadata.h
+++ b/include/swift/ABI/Metadata.h
@@ -1495,7 +1495,11 @@ struct TargetTupleTypeMetadata : public TargetMetadata<Runtime> {
     ConstTargetMetadataPointer<Runtime, swift::TargetMetadata> Type;
 
     /// The offset of the tuple element within the tuple.
+#if __APPLE__
     StoredSize Offset;
+#else
+    uint32_t Offset;
+#endif
 
     OpaqueValue *findIn(OpaqueValue *tuple) const {
       return (OpaqueValue*) (((char*) tuple) + Offset);
@@ -1506,6 +1510,9 @@ struct TargetTupleTypeMetadata : public TargetMetadata<Runtime> {
     }
   };
 
+  static_assert(sizeof(Element) == sizeof(StoredSize) * 2,
+                "element size should be two words");
+
   Element *getElements() {
     return reinterpret_cast<Element*>(this + 1);
   }
diff --git a/lib/IRGen/IRGenModule.cpp b/lib/IRGen/IRGenModule.cpp
index 1cfb741f44928..fae7bd56c34e9 100644
--- a/lib/IRGen/IRGenModule.cpp
+++ b/lib/IRGen/IRGenModule.cpp
@@ -266,7 +266,7 @@ IRGenModule::IRGenModule(IRGenerator &irgen,
   // A tuple type metadata record has a couple extra fields.
   auto tupleElementTy = createStructType(*this, "swift.tuple_element_type", {
     TypeMetadataPtrTy,      // Metadata *Type;
-    SizeTy                  // size_t Offset;
+    Int32Ty                 // int32_t Offset;
   });
   TupleTypeMetadataPtrTy = createStructPointerType(*this, "swift.tuple_type", {
     TypeMetadataStructTy,   // (base)
diff --git a/test/IRGen/generic_tuples.swift b/test/IRGen/generic_tuples.swift
index ed6dca3e1f0ac..f1a7b00b7c184 100644
--- a/test/IRGen/generic_tuples.swift
+++ b/test/IRGen/generic_tuples.swift
@@ -9,7 +9,7 @@
 // CHECK: [[TYPE:%swift.type]] = type {
 // CHECK: [[OPAQUE:%swift.opaque]] = type opaque
 // CHECK: [[TUPLE_TYPE:%swift.tuple_type]] = type { [[TYPE]], i64, i8*, [0 x %swift.tuple_element_type] }
-// CHECK: %swift.tuple_element_type = type { [[TYPE]]*, i64 }
+// CHECK: %swift.tuple_element_type = type { [[TYPE]]*, i32 }
 
 func dup<T>(_ x: T) -> (T, T) { var x = x; return (x,x) }
 // CHECK:    define hidden swiftcc void @"$s14generic_tuples3dupyx_xtxlF"(%swift.opaque* noalias nocapture, %swift.opaque* noalias nocapture, %swift.opaque* noalias nocapture, %swift.type* %T)