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
@@ -679,5 +679,8 @@
   return std::nullopt;
 }
 
+// Returns "m" for a module, "m:sm" for a submodule.
+std::string GetModuleOrSubmoduleName(const Symbol &);
+
 } // namespace Fortran::semantics
 #endif // FORTRAN_SEMANTICS_TOOLS_H_
diff --git a/flang/lib/Semantics/check-declarations.cpp b/flang/lib/Semantics/check-declarations.cpp
--- a/flang/lib/Semantics/check-declarations.cpp
+++ b/flang/lib/Semantics/check-declarations.cpp
@@ -3133,26 +3133,22 @@
       (procClass == ProcedureDefinitionClass::Module &&
           symbol.attrs().test(Attr::MODULE)) &&
       !subprogram->bindName() && !subprogram->isInterface()) {
-    const Symbol *module{nullptr};
-    if (const Scope * moduleScope{FindModuleContaining(symbol.owner())};
-        moduleScope && moduleScope->symbol()) {
-      if (const auto *details{
-              moduleScope->symbol()->detailsIf<ModuleDetails>()}) {
-        if (details->parent()) {
-          moduleScope = details->parent();
-        }
-        module = moduleScope->symbol();
-      }
-    }
-    if (module) {
+    const Symbol &interface {
+      subprogram->moduleInterface() ? *subprogram->moduleInterface() : symbol
+    };
+    if (const Symbol *
+            module{interface.owner().kind() == Scope::Kind::Module
+                    ? interface.owner().symbol()
+                    : nullptr};
+        module && module->has<ModuleDetails>()) {
       std::pair<SourceName, const Symbol *> key{symbol.name(), module};
       auto iter{moduleProcs_.find(key)};
       if (iter == moduleProcs_.end()) {
         moduleProcs_.emplace(std::move(key), symbol);
       } else if (
           auto *msg{messages_.Say(symbol.name(),
-              "Module procedure '%s' in module '%s' has multiple definitions"_err_en_US,
-              symbol.name(), module->name())}) {
+              "Module procedure '%s' in '%s' has multiple definitions"_err_en_US,
+              symbol.name(), GetModuleOrSubmoduleName(*module))}) {
         msg->Attach(iter->second->name(), "Previous definition of '%s'"_en_US,
             symbol.name());
       }
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
@@ -1646,4 +1646,13 @@
   return false;
 }
 
+std::string GetModuleOrSubmoduleName(const Symbol &symbol) {
+  const auto &details{symbol.get<ModuleDetails>()};
+  std::string result{symbol.name().ToString()};
+  if (details.ancestor() && details.ancestor()->symbol()) {
+    result = details.ancestor()->symbol()->name().ToString() + ':' + result;
+  }
+  return result;
+}
+
 } // namespace Fortran::semantics
diff --git a/flang/test/Semantics/separate-mp04.f90 b/flang/test/Semantics/separate-mp04.f90
--- a/flang/test/Semantics/separate-mp04.f90
+++ b/flang/test/Semantics/separate-mp04.f90
@@ -28,17 +28,17 @@
 
 submodule(m1) sm2
  contains
-  !ERROR: Module procedure 'x002' in module 'm1' has multiple definitions
+  !ERROR: Module procedure 'x002' in 'm1' has multiple definitions
   module subroutine x002
   end subroutine
 end
 
 submodule(m1:sm2) sm3
  contains
-  !ERROR: Module procedure 'x002' in module 'm1' has multiple definitions
+  !ERROR: Module procedure 'x002' in 'm1' has multiple definitions
   module subroutine x002
   end subroutine
-  !ERROR: Module procedure 'x003' in module 'm1' has multiple definitions
+  !ERROR: Module procedure 'x003' in 'm1' has multiple definitions
   module subroutine x003
   end subroutine
 end
@@ -51,7 +51,7 @@
 
 submodule(m1:sm1) sm5
  contains
-  !ERROR: Module procedure 'x004' in module 'm1' has multiple definitions
+  !ERROR: Module procedure 'x004' in 'm1:sm1' has multiple definitions
   module subroutine x004
   end subroutine
 end