Index: include/clang/Serialization/ASTReader.h
===================================================================
--- include/clang/Serialization/ASTReader.h
+++ include/clang/Serialization/ASTReader.h
@@ -984,14 +984,26 @@
   /// \brief The generation number of each identifier, which keeps track of
   /// the last time we loaded information about this identifier.
   llvm::DenseMap<IdentifierInfo *, unsigned> IdentifierGeneration;
-  
-  /// \brief Contains declarations and definitions that will be
+
+  class InterestingDecl {
+    Decl *D;
+    bool DeclHasPendingBody;
+
+  public:
+    InterestingDecl(Decl *D, bool HasBody)
+        : D(D), DeclHasPendingBody(HasBody) {}
+    Decl *getDecl() { return D; }
+    /// Whether the declaration has a pending body.
+    bool hasPendingBody() { return DeclHasPendingBody; }
+  };
+
+  /// \brief Contains declarations and definitions that could be
   /// "interesting" to the ASTConsumer, when we get that AST consumer.
   ///
   /// "Interesting" declarations are those that have data that may
   /// need to be emitted, such as inline function definitions or
   /// Objective-C protocols.
-  std::deque<Decl *> InterestingDecls;
+  std::deque<InterestingDecl> PotentiallyInterestingDecls;
 
   /// \brief The list of redeclaration chains that still need to be 
   /// reconstructed, and the local offset to the corresponding list
Index: lib/Serialization/ASTReader.cpp
===================================================================
--- lib/Serialization/ASTReader.cpp
+++ lib/Serialization/ASTReader.cpp
@@ -7191,31 +7191,6 @@
   Consumer->HandleInterestingDecl(DeclGroupRef(ImplD));
 }
 
-void ASTReader::PassInterestingDeclsToConsumer() {
-  assert(Consumer);
-
-  if (PassingDeclsToConsumer)
-    return;
-
-  // Guard variable to avoid recursively redoing the process of passing
-  // decls to consumer.
-  SaveAndRestore<bool> GuardPassingDeclsToConsumer(PassingDeclsToConsumer,
-                                                   true);
-
-  // Ensure that we've loaded all potentially-interesting declarations
-  // that need to be eagerly loaded.
-  for (auto ID : EagerlyDeserializedDecls)
-    GetDecl(ID);
-  EagerlyDeserializedDecls.clear();
-
-  while (!InterestingDecls.empty()) {
-    Decl *D = InterestingDecls.front();
-    InterestingDecls.pop_front();
-
-    PassInterestingDeclToConsumer(D);
-  }
-}
-
 void ASTReader::PassInterestingDeclToConsumer(Decl *D) {
   if (ObjCImplDecl *ImplD = dyn_cast<ObjCImplDecl>(D))
     PassObjCImplDeclToConsumer(ImplD, Consumer);
Index: lib/Serialization/ASTReaderDecl.cpp
===================================================================
--- lib/Serialization/ASTReaderDecl.cpp
+++ lib/Serialization/ASTReaderDecl.cpp
@@ -3609,12 +3609,37 @@
   // AST consumer might need to know about, queue it.
   // We don't pass it to the consumer immediately because we may be in recursive
   // loading, and some declarations may still be initializing.
-  if (isConsumerInterestedIn(Context, D, Reader.hasPendingBody()))
-    InterestingDecls.push_back(D);
+  PotentiallyInterestingDecls.push_back(
+      InterestingDecl(D, Reader.hasPendingBody()));
 
   return D;
 }
 
+void ASTReader::PassInterestingDeclsToConsumer() {
+  assert(Consumer);
+
+  if (PassingDeclsToConsumer)
+    return;
+
+  // Guard variable to avoid recursively redoing the process of passing
+  // decls to consumer.
+  SaveAndRestore<bool> GuardPassingDeclsToConsumer(PassingDeclsToConsumer,
+                                                   true);
+
+  // Ensure that we've loaded all potentially-interesting declarations
+  // that need to be eagerly loaded.
+  for (auto ID : EagerlyDeserializedDecls)
+    GetDecl(ID);
+  EagerlyDeserializedDecls.clear();
+
+  while (!PotentiallyInterestingDecls.empty()) {
+    InterestingDecl D = PotentiallyInterestingDecls.front();
+    PotentiallyInterestingDecls.pop_front();
+    if (isConsumerInterestedIn(Context, D.getDecl(), D.hasPendingBody()))
+      PassInterestingDeclToConsumer(D.getDecl());
+  }
+}
+
 void ASTReader::loadDeclUpdateRecords(serialization::DeclID ID, Decl *D) {
   // The declaration may have been modified by files later in the chain.
   // If this is the case, read the record containing the updates from each file
@@ -3625,6 +3650,9 @@
     auto UpdateOffsets = std::move(UpdI->second);
     DeclUpdateOffsets.erase(UpdI);
 
+    // FIXME: This call to isConsumerInterestedIn is not safe because
+    // we could be deserializing declarations at the moment. We should
+    // delay calling this in the same way as done in D30793.
     bool WasInteresting = isConsumerInterestedIn(Context, D, false);
     for (auto &FileAndOffset : UpdateOffsets) {
       ModuleFile *F = FileAndOffset.first;
@@ -3646,7 +3674,8 @@
       // we need to hand it off to the consumer.
       if (!WasInteresting &&
           isConsumerInterestedIn(Context, D, Reader.hasPendingBody())) {
-        InterestingDecls.push_back(D);
+        PotentiallyInterestingDecls.push_back(
+            InterestingDecl(D, Reader.hasPendingBody()));
         WasInteresting = true;
       }
     }
Index: test/Modules/Inputs/PR32186/a.h
===================================================================
--- /dev/null
+++ test/Modules/Inputs/PR32186/a.h
@@ -0,0 +1,20 @@
+#pragma once
+
+template <class T>
+struct base {
+  inline static constexpr T max() noexcept { return 10; }
+};
+
+template <typename T>
+static const constexpr T highest = base<T>::max();
+
+template <bool v>
+using cond_t = int;
+
+template <unsigned N>
+using dep_t = cond_t<(N < highest<int>)>;
+
+template <unsigned N>
+struct foo {
+  using type = dep_t<N>;
+};
Index: test/Modules/Inputs/PR32186/module.modulemap
===================================================================
--- /dev/null
+++ test/Modules/Inputs/PR32186/module.modulemap
@@ -0,0 +1 @@
+module a { header "a.h" export * }
Index: test/Modules/Inputs/delay-emit-check/Module.h
===================================================================
--- /dev/null
+++ test/Modules/Inputs/delay-emit-check/Module.h
@@ -0,0 +1,6 @@
+namespace a {
+namespace b {
+int foo();
+const int x = foo();
+}
+}
Index: test/Modules/Inputs/delay-emit-check/module.modulemap
===================================================================
--- /dev/null
+++ test/Modules/Inputs/delay-emit-check/module.modulemap
@@ -0,0 +1 @@
+module "a" { header "Module.h" }
Index: test/Modules/delay-emit-check-PR32186.cpp
===================================================================
--- /dev/null
+++ test/Modules/delay-emit-check-PR32186.cpp
@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -x c++ -fmodules-cache-path=%t -std=c++1z -fmodules -I%S/Inputs/PR32186/ -fmodule-map-file=%S/Inputs/PR32186/module.modulemap %s
+
+#include <a.h>
+
+template struct foo<10>;
+int main() { return 0; }
Index: test/Modules/delay-emit-check.cpp
===================================================================
--- /dev/null
+++ test/Modules/delay-emit-check.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -fmodules-cache-path=%t/cache -fmodules -fimplicit-module-maps -emit-obj -I%S/Inputs/delay-emit-check/ %s -o %t.o
+
+// Test that we don't make unsafe calls such as to DeclMustBeEmitted during
+// deserialization.
+
+namespace a {
+namespace b {
+int foo();
+}
+}
+#include "Module.h"
Index: test/PCH/Inputs/empty-def-fwd-struct.modulemap
===================================================================
--- /dev/null
+++ test/PCH/Inputs/empty-def-fwd-struct.modulemap
@@ -0,0 +1,2 @@
+module M { header "../empty-def-fwd-struct.h" }
+
Index: test/PCH/delay-PCH-emit-check.cpp
===================================================================
--- /dev/null
+++ test/PCH/delay-PCH-emit-check.cpp
@@ -0,0 +1,4 @@
+// RUN: %clang_cc1 -x c++ -std=c++14 -fmodules -emit-module -fmodule-name=M %S/Inputs/empty-def-fwd-struct.modulemap -o %t.pcm
+// RUN: %clang_cc1 -x c++ -std=c++14 -fmodules -emit-llvm -fmodule-file=%t.pcm %s -o %t.o
+
+#include "empty-def-fwd-struct.h"