diff --git a/lib/SIL/IR/SILType.cpp b/lib/SIL/IR/SILType.cpp
index e3feb8378fe7c..57caf3d5277b9 100644
--- a/lib/SIL/IR/SILType.cpp
+++ b/lib/SIL/IR/SILType.cpp
@@ -851,6 +851,16 @@ bool SILType::isLoweringOf(TypeExpansionContext context, SILModule &Mod,
     }
   }
 
+  // The pattern of a pack expansion is lowered.
+  if (auto formalExpansion = dyn_cast<PackExpansionType>(formalType)) {
+    if (auto loweredExpansion = loweredType.getAs<PackExpansionType>()) {
+      return loweredExpansion.getCountType() == formalExpansion.getCountType()
+         && SILType::getPrimitiveAddressType(loweredExpansion.getPatternType())
+               .isLoweringOf(context, Mod, formalExpansion.getPatternType());
+    }
+    return false;
+  }
+
   // Dynamic self has the same lowering as its contained type.
   if (auto dynamicSelf = dyn_cast<DynamicSelfType>(formalType))
     formalType = dynamicSelf.getSelfType();
diff --git a/test/SILGen/variadic-generic-tuples.swift b/test/SILGen/variadic-generic-tuples.swift
index 300c599d969ff..c5d97cfd0713e 100644
--- a/test/SILGen/variadic-generic-tuples.swift
+++ b/test/SILGen/variadic-generic-tuples.swift
@@ -352,3 +352,18 @@ func testStructOfLoadableTuple() -> StructOfLoadableTuple<Int> {
 // CHECK-NEXT:    [[PACK_ELT_ADDR:%.*]] = pack_element_get [[INDEX]] of %1 : $*Pack{repeat GenericButLoadable<each S, each S>} as $*GenericButLoadable<@pack_element([[UUID]]) each S, @pack_element([[UUID]]) each S>
 // CHECK-NEXT:    [[PACK_ELT:%.*]] = load [trivial] [[PACK_ELT_ADDR]] :
 // CHECK-NEXT:    store [[PACK_ELT]] to [trivial] [[TUPLE_ELT_ADDR]] :
+
+// rdar://107290521
+//   The verifier had some home-grown type-lowering logic that didn't
+//   know about pack expansions.
+// CHECK-LABEL: sil {{.*}}@$s4main22testExistentialErasureyyxxQpRvzlF1gL_yyqd__qd__QpRvzRvd__r__lF :
+// CHECK:         [[T0:%.*]] = init_existential_addr {{.*}} : $*Any, $(repeat each T.Type)
+// CHECK:         tuple_pack_element_addr {{.*}} of [[T0]] : $*(repeat @thick each T.Type) as $*@thick (@pack_element("{{.*}}") each T).Type
+func testExistentialErasure<each T>(_: repeat each T) {
+  func g<each U>(_: repeat each U) {
+    print((repeat (each T).self))
+    print((repeat (each U).self))
+  }
+
+  g(1, "hi", false)
+}