diff --git a/flang/include/flang/Semantics/tools.h b/flang/include/flang/Semantics/tools.h
--- a/flang/include/flang/Semantics/tools.h
+++ b/flang/include/flang/Semantics/tools.h
@@ -30,9 +30,14 @@
 class Scope;
 class Symbol;
 
+// Note: Here ProgramUnit includes internal subprograms while TopLevelUnit
+// does not. "program-unit" in the Fortran standard matches TopLevelUnit.
+const Scope &GetTopLevelUnitContaining(const Scope &);
+const Scope &GetTopLevelUnitContaining(const Symbol &);
+const Scope &GetProgramUnitContaining(const Scope &);
+const Scope &GetProgramUnitContaining(const Symbol &);
+
 const Scope *FindModuleContaining(const Scope &);
-const Scope *FindProgramUnitContaining(const Scope &);
-const Scope *FindProgramUnitContaining(const Symbol &);
 const Scope *FindPureProcedureContaining(const Scope &);
 const Scope *FindPureProcedureContaining(const Symbol &);
 const Symbol *FindPointerComponent(const Scope &);
diff --git a/flang/lib/Semantics/check-return.cpp b/flang/lib/Semantics/check-return.cpp
--- a/flang/lib/Semantics/check-return.cpp
+++ b/flang/lib/Semantics/check-return.cpp
@@ -16,11 +16,10 @@
 namespace Fortran::semantics {
 
 static const Scope *FindContainingSubprogram(const Scope &start) {
-  const Scope *scope{FindProgramUnitContaining(start)};
-  return scope &&
-          (scope->kind() == Scope::Kind::MainProgram ||
-              scope->kind() == Scope::Kind::Subprogram)
-      ? scope
+  const Scope &scope{GetProgramUnitContaining(start)};
+  return scope.kind() == Scope::Kind::MainProgram ||
+          scope.kind() == Scope::Kind::Subprogram
+      ? &scope
       : nullptr;
 }
 
diff --git a/flang/lib/Semantics/resolve-names.cpp b/flang/lib/Semantics/resolve-names.cpp
--- a/flang/lib/Semantics/resolve-names.cpp
+++ b/flang/lib/Semantics/resolve-names.cpp
@@ -5602,11 +5602,11 @@
 }
 
 bool DeclarationVisitor::IsUplevelReference(const Symbol &symbol) {
-  const Scope *symbolUnit{FindProgramUnitContaining(symbol)};
-  if (symbolUnit == FindProgramUnitContaining(currScope())) {
+  const Scope &symbolUnit{GetProgramUnitContaining(symbol)};
+  if (symbolUnit == GetProgramUnitContaining(currScope())) {
     return false;
   } else {
-    Scope::Kind kind{DEREF(symbolUnit).kind()};
+    Scope::Kind kind{symbolUnit.kind()};
     return kind == Scope::Kind::Subprogram || kind == Scope::Kind::MainProgram;
   }
 }
diff --git a/flang/lib/Semantics/tools.cpp b/flang/lib/Semantics/tools.cpp
--- a/flang/lib/Semantics/tools.cpp
+++ b/flang/lib/Semantics/tools.cpp
@@ -37,13 +37,24 @@
   }
 }
 
+const Scope &GetTopLevelUnitContaining(const Scope &start) {
+  CHECK(!start.IsGlobal());
+  return DEREF(FindScopeContaining(
+      start, [](const Scope &scope) { return scope.parent().IsGlobal(); }));
+}
+
+const Scope &GetTopLevelUnitContaining(const Symbol &symbol) {
+  return GetTopLevelUnitContaining(symbol.owner());
+}
+
 const Scope *FindModuleContaining(const Scope &start) {
   return FindScopeContaining(
       start, [](const Scope &scope) { return scope.IsModule(); });
 }
 
-const Scope *FindProgramUnitContaining(const Scope &start) {
-  return FindScopeContaining(start, [](const Scope &scope) {
+const Scope &GetProgramUnitContaining(const Scope &start) {
+  CHECK(!start.IsGlobal());
+  return DEREF(FindScopeContaining(start, [](const Scope &scope) {
     switch (scope.kind()) {
     case Scope::Kind::Module:
     case Scope::Kind::MainProgram:
@@ -53,23 +64,19 @@
     default:
       return false;
     }
-  });
+  }));
 }
 
-const Scope *FindProgramUnitContaining(const Symbol &symbol) {
-  return FindProgramUnitContaining(symbol.owner());
+const Scope &GetProgramUnitContaining(const Symbol &symbol) {
+  return GetProgramUnitContaining(symbol.owner());
 }
 
 const Scope *FindPureProcedureContaining(const Scope &start) {
   // N.B. We only need to examine the innermost containing program unit
   // because an internal subprogram of a pure subprogram must also
   // be pure (C1592).
-  if (const Scope * scope{FindProgramUnitContaining(start)}) {
-    if (IsPureProcedure(*scope)) {
-      return scope;
-    }
-  }
-  return nullptr;
+  const Scope &scope{GetProgramUnitContaining(start)};
+  return IsPureProcedure(scope) ? &scope : nullptr;
 }
 
 Tristate IsDefinedAssignment(
@@ -176,9 +183,9 @@
 }
 
 bool IsUseAssociated(const Symbol &symbol, const Scope &scope) {
-  const Scope *owner{FindProgramUnitContaining(symbol.GetUltimate().owner())};
-  return owner && owner->kind() == Scope::Kind::Module &&
-      owner != FindProgramUnitContaining(scope);
+  const Scope &owner{GetProgramUnitContaining(symbol.GetUltimate().owner())};
+  return owner.kind() == Scope::Kind::Module &&
+      owner != GetProgramUnitContaining(scope);
 }
 
 bool DoesScopeContain(
@@ -203,10 +210,9 @@
 }
 
 bool IsHostAssociated(const Symbol &symbol, const Scope &scope) {
-  const Scope *subprogram{FindProgramUnitContaining(scope)};
-  return subprogram &&
-      DoesScopeContain(
-          FindProgramUnitContaining(FollowHostAssoc(symbol)), *subprogram);
+  const Scope &subprogram{GetProgramUnitContaining(scope)};
+  return DoesScopeContain(
+      &GetProgramUnitContaining(FollowHostAssoc(symbol)), subprogram);
 }
 
 bool IsInStmtFunction(const Symbol &symbol) {