diff --git a/lib/Serialization/Deserialization.cpp b/lib/Serialization/Deserialization.cpp
index ef371a520ce13..f9992f5ff963b 100644
--- a/lib/Serialization/Deserialization.cpp
+++ b/lib/Serialization/Deserialization.cpp
@@ -4848,7 +4848,9 @@ class TypeDeserializer {
     auto substitutedType = substitutedTypeOrError.get();
 
     // Read the substitutions.
-    auto subMap = MF.getSubstitutionMap(substitutionsID);
+    auto subMapOrError = MF.getSubstitutionMapChecked(substitutionsID);
+    if (!subMapOrError)
+      return subMapOrError.takeError();
 
     auto parentTypeOrError = MF.getTypeChecked(parentTypeID);
     if (!parentTypeOrError)
@@ -4858,11 +4860,12 @@ class TypeDeserializer {
     if (alias &&
         alias->getAttrs().isUnavailable(ctx) &&
         alias->isCompatibilityAlias()) {
-      return alias->getUnderlyingType().subst(subMap);
+      return alias->getUnderlyingType().subst(subMapOrError.get());
     }
 
     auto parentType = parentTypeOrError.get();
-    return TypeAliasType::get(alias, parentType, subMap, substitutedType);
+    return TypeAliasType::get(alias, parentType, subMapOrError.get(),
+                              substitutedType);
   }
 
   Expected<Type> deserializeNominalType(ArrayRef<uint64_t> scratch,
@@ -5180,9 +5183,11 @@ class TypeDeserializer {
       return opaqueTypeOrError.takeError();
 
     auto opaqueDecl = cast<OpaqueTypeDecl>(opaqueTypeOrError.get());
-    auto subs = MF.getSubstitutionMap(subsID);
+    auto subsOrError = MF.getSubstitutionMapChecked(subsID);
+    if (!subsOrError)
+      return subsOrError.takeError();
 
-    return OpaqueTypeArchetypeType::get(opaqueDecl, subs);
+    return OpaqueTypeArchetypeType::get(opaqueDecl, subsOrError.get());
   }
       
   Expected<Type> deserializeNestedArchetypeType(ArrayRef<uint64_t> scratch,
@@ -5317,8 +5322,11 @@ class TypeDeserializer {
     if (!layout)
       return nullptr;
 
-    auto subMap = MF.getSubstitutionMap(subMapID);
-    return SILBoxType::get(ctx, layout, subMap);
+    auto subMapOrError = MF.getSubstitutionMapChecked(subMapID);
+    if (!subMapOrError)
+      return subMapOrError.takeError();
+
+    return SILBoxType::get(ctx, layout, subMapOrError.get());
   }
 
   Expected<Type> deserializeSILFunctionType(ArrayRef<uint64_t> scratch,
@@ -5503,16 +5511,19 @@ class TypeDeserializer {
 
     GenericSignature invocationSig =
       MF.getGenericSignature(rawInvocationGenericSig);
-    SubstitutionMap invocationSubs =
-      MF.getSubstitutionMap(rawInvocationSubs).getCanonical();
-    SubstitutionMap patternSubs =
-      MF.getSubstitutionMap(rawPatternSubs).getCanonical();
+    auto invocationSubsOrErr = MF.getSubstitutionMapChecked(rawInvocationSubs);
+    if (!invocationSubsOrErr)
+      return invocationSubsOrErr.takeError();
+    auto patternSubsOrErr = MF.getSubstitutionMapChecked(rawPatternSubs);
+    if (!patternSubsOrErr)
+      return patternSubsOrErr.takeError();
 
     return SILFunctionType::get(invocationSig, extInfo, coroutineKind.getValue(),
                                 calleeConvention.getValue(),
                                 allParams, allYields, allResults,
                                 errorResult,
-                                patternSubs, invocationSubs,
+                                patternSubsOrErr.get().getCanonical(),
+                                invocationSubsOrErr.get().getCanonical(),
                                 ctx, witnessMethodConformance);
   }