diff --git a/flang/include/flang/Semantics/scope.h b/flang/include/flang/Semantics/scope.h
index 0c5beb6492c6d..48109c9de0412 100644
--- a/flang/include/flang/Semantics/scope.h
+++ b/flang/include/flang/Semantics/scope.h
@@ -247,7 +247,7 @@ class Scope {
 
   // The range of the source of this and nested scopes.
   const parser::CharBlock &sourceRange() const { return sourceRange_; }
-  void AddSourceRange(const parser::CharBlock &);
+  void AddSourceRange(parser::CharBlock);
   // Find the smallest scope under this one that contains source
   const Scope *FindScope(parser::CharBlock) const;
   Scope *FindScope(parser::CharBlock);
@@ -276,6 +276,7 @@ class Scope {
   std::size_t size_{0}; // size in bytes
   std::optional<std::size_t> alignment_; // required alignment in bytes
   parser::CharBlock sourceRange_;
+  const parser::CookedSource *cookedSource_{nullptr};
   Symbol *const symbol_; // if not null, symbol_->scope() == this
   std::list<Scope> children_;
   mapType symbols_;
diff --git a/flang/lib/Semantics/scope.cpp b/flang/lib/Semantics/scope.cpp
index bcffbd331280c..7570714732e1a 100644
--- a/flang/lib/Semantics/scope.cpp
+++ b/flang/lib/Semantics/scope.cpp
@@ -8,6 +8,7 @@
 
 #include "flang/Semantics/scope.h"
 #include "flang/Parser/characters.h"
+#include "flang/Semantics/semantics.h"
 #include "flang/Semantics/symbol.h"
 #include "flang/Semantics/type.h"
 #include "llvm/Support/raw_ostream.h"
@@ -309,7 +310,7 @@ const Scope *Scope::FindScope(parser::CharBlock source) const {
 
 Scope *Scope::FindScope(parser::CharBlock source) {
   bool isContained{sourceRange_.Contains(source)};
-  if (!isContained && !IsTopLevel() && !IsModuleFile()) {
+  if (!isContained && !IsTopLevel() && kind_ != Kind::Module) {
     return nullptr;
   }
   for (auto &child : children_) {
@@ -320,9 +321,49 @@ Scope *Scope::FindScope(parser::CharBlock source) {
   return isContained && !IsTopLevel() ? this : nullptr;
 }
 
-void Scope::AddSourceRange(const parser::CharBlock &source) {
-  for (auto *scope{this}; !scope->IsGlobal(); scope = &scope->parent()) {
-    scope->sourceRange_.ExtendToCover(source);
+void Scope::AddSourceRange(parser::CharBlock source) {
+  if (source.empty()) {
+    return;
+  }
+  const parser::AllCookedSources &allCookedSources{context_.allCookedSources()};
+  const parser::CookedSource *cooked{allCookedSources.Find(source)};
+  if (!cooked) {
+    CHECK(context_.IsTempName(source.ToString()));
+    return;
+  }
+  for (auto *scope{this}; !scope->IsTopLevel(); scope = &scope->parent()) {
+    CHECK(scope->sourceRange_.empty() == (scope->cookedSource_ == nullptr));
+    if (!scope->cookedSource_) {
+      scope->cookedSource_ = cooked;
+      scope->sourceRange_ = source;
+    } else if (scope->cookedSource_ == cooked) {
+      scope->sourceRange_.ExtendToCover(source);
+    } else {
+      // There's a bug that will be hard to fix; crash informatively
+      const parser::AllSources &allSources{allCookedSources.allSources()};
+      const auto describe{[&](parser::CharBlock src) {
+        if (auto range{allCookedSources.GetProvenanceRange(src)}) {
+          std::size_t offset;
+          if (const parser::SourceFile *
+              file{allSources.GetSourceFile(range->start(), &offset)}) {
+            return "'"s + file->path() + "' at " + std::to_string(offset) +
+                " for " + std::to_string(range->size());
+          } else {
+            return "(GetSourceFile failed)"s;
+          }
+        } else {
+          return "(GetProvenanceRange failed)"s;
+        }
+      }};
+      std::string scopeDesc{describe(scope->sourceRange_)};
+      std::string newDesc{describe(source)};
+      common::die("AddSourceRange would have combined ranges from distinct "
+                  "source files \"%s\" and \"%s\"",
+          scopeDesc.c_str(), newDesc.c_str());
+    }
+    if (scope->IsSubmodule()) {
+      break; // Submodules are child scopes but not contained ranges
+    }
   }
 }