Index: flang/include/flang/Semantics/symbol.h
===================================================================
--- flang/include/flang/Semantics/symbol.h
+++ flang/include/flang/Semantics/symbol.h
@@ -94,6 +94,9 @@
   void add_alternateReturn() { dummyArgs_.push_back(nullptr); }
   const MaybeExpr &stmtFunction() const { return stmtFunction_; }
   void set_stmtFunction(SomeExpr &&expr) { stmtFunction_ = std::move(expr); }
+  Symbol *moduleInterface() { return moduleInterface_; }
+  const Symbol *moduleInterface() const { return moduleInterface_; }
+  void set_moduleInterface(Symbol &);
 
 private:
   bool isInterface_{false}; // true if this represents an interface-body
@@ -102,6 +105,11 @@
   Symbol *result_{nullptr};
   Scope *entryScope_{nullptr}; // if ENTRY, points to subprogram's scope
   MaybeExpr stmtFunction_;
+  // For MODULE FUNCTION or SUBROUTINE, this is the symbol of its declared
+  // interface.  For MODULE PROCEDURE, this is the declared interface if it
+  // appeared in an ancestor (sub)module.
+  Symbol *moduleInterface_{nullptr};
+
   friend llvm::raw_ostream &operator<<(
       llvm::raw_ostream &, const SubprogramDetails &);
 };
Index: flang/lib/Semantics/check-declarations.cpp
===================================================================
--- flang/lib/Semantics/check-declarations.cpp
+++ flang/lib/Semantics/check-declarations.cpp
@@ -2136,6 +2136,21 @@
   if (!proc1 || !proc2) {
     return;
   }
+  if (proc1->attrs.test(Procedure::Attr::Pure) !=
+      proc2->attrs.test(Procedure::Attr::Pure)) {
+    Say(symbol1, symbol2,
+        "Module subprogram '%s' and its corresponding interface body are not both PURE"_err_en_US);
+  }
+  if (proc1->attrs.test(Procedure::Attr::Elemental) !=
+      proc2->attrs.test(Procedure::Attr::Elemental)) {
+    Say(symbol1, symbol2,
+        "Module subprogram '%s' and its corresponding interface body are not both ELEMENTAL"_err_en_US);
+  }
+  if (proc1->attrs.test(Procedure::Attr::BindC) !=
+      proc2->attrs.test(Procedure::Attr::BindC)) {
+    Say(symbol1, symbol2,
+        "Module subprogram '%s' and its corresponding interface body are not both BIND(C)"_err_en_US);
+  }
   if (proc1->functionResult && proc2->functionResult &&
       *proc1->functionResult != *proc2->functionResult) {
     Say(symbol1, symbol2,
Index: flang/lib/Semantics/resolve-names.cpp
===================================================================
--- flang/lib/Semantics/resolve-names.cpp
+++ flang/lib/Semantics/resolve-names.cpp
@@ -3317,13 +3317,21 @@
     Say(name, "'%s' was not declared a separate module procedure"_err_en_US);
     return false;
   }
-  if (symbol->owner() == currScope()) {
-    PushScope(Scope::Kind::Subprogram, symbol);
+  if (symbol->owner() == currScope() && symbol->scope()) {
+    // This is a MODULE PROCEDURE whose interface appears in its host.
+    // Convert the module procedure's interface into a subprogram.
+    SetScope(DEREF(symbol->scope()));
+    symbol->get<SubprogramDetails>().set_isInterface(false);
+    if (IsFunction(*symbol)) {
+      funcInfoStack_.emplace_back(); // just to be popped later
+    }
   } else {
+    // Copy the interface into a new subprogram scope.
     Symbol &newSymbol{MakeSymbol(name, SubprogramDetails{})};
     PushScope(Scope::Kind::Subprogram, &newSymbol);
     const auto &details{symbol->get<SubprogramDetails>()};
     auto &newDetails{newSymbol.get<SubprogramDetails>()};
+    newDetails.set_moduleInterface(*symbol);
     for (const Symbol *dummyArg : details.dummyArgs()) {
       if (!dummyArg) {
         newDetails.add_alternateReturn();
@@ -3349,14 +3357,34 @@
         "MODULE or SUBMODULE"_err_en_US);
     return false;
   }
-
-  if (hasModulePrefix && !inInterfaceBlock() &&
-      !IsSeparateModuleProcedureInterface(
-          FindSymbol(currScope().parent(), name))) {
-    Say(name, "'%s' was not declared a separate module procedure"_err_en_US);
-    return false;
+  Symbol *moduleInterface{nullptr};
+  if (hasModulePrefix && !inInterfaceBlock()) {
+    moduleInterface = FindSymbol(currScope(), name);
+    if (IsSeparateModuleProcedureInterface(moduleInterface)) {
+      // Subprogram is MODULE FUNCTION or MODULE SUBROUTINE with an interface
+      // previously defined in the same scope.
+      currScope().erase(moduleInterface->name());
+    } else {
+      moduleInterface = nullptr;
+    }
+    if (!moduleInterface) {
+      moduleInterface = FindSymbol(currScope().parent(), name);
+      if (!IsSeparateModuleProcedureInterface(moduleInterface)) {
+        Say(name,
+            "'%s' was not declared a separate module procedure"_err_en_US);
+        return false;
+      }
+    }
+  }
+  Symbol &newSymbol{PushSubprogramScope(name, subpFlag)};
+  if (moduleInterface) {
+    newSymbol.get<SubprogramDetails>().set_moduleInterface(*moduleInterface);
+    if (moduleInterface->attrs().test(Attr::PRIVATE)) {
+      newSymbol.attrs().set(Attr::PRIVATE);
+    } else if (moduleInterface->attrs().test(Attr::PUBLIC)) {
+      newSymbol.attrs().set(Attr::PUBLIC);
+    }
   }
-  PushSubprogramScope(name, subpFlag);
   if (IsFunction(currScope())) {
     funcInfoStack_.emplace_back();
   }
@@ -7059,7 +7087,12 @@
       node.IsModule() ? SubprogramKind::Module : SubprogramKind::Internal};
   for (auto &child : node.children()) {
     auto &symbol{MakeSymbol(child.name(), SubprogramNameDetails{kind, child})};
-    symbol.set(child.GetSubpFlag());
+    auto childKind{child.GetKind()};
+    if (childKind == ProgramTree::Kind::Function) {
+      symbol.set(Symbol::Flag::Function);
+    } else if (childKind == ProgramTree::Kind::Subroutine) {
+      symbol.set(Symbol::Flag::Subroutine);
+    }
     for (const auto &entryStmt : child.entryStmts()) {
       SubprogramNameDetails details{kind, child};
       details.set_isEntryStmt();
Index: flang/lib/Semantics/symbol.cpp
===================================================================
--- flang/lib/Semantics/symbol.cpp
+++ flang/lib/Semantics/symbol.cpp
@@ -70,6 +70,11 @@
   }
 }
 
+void SubprogramDetails::set_moduleInterface(Symbol &symbol) {
+  CHECK(!moduleInterface_);
+  moduleInterface_ = &symbol;
+}
+
 const Scope *ModuleDetails::parent() const {
   return isSubmodule_ && scope_ ? &scope_->parent() : nullptr;
 }
@@ -117,6 +122,9 @@
   if (x.stmtFunction_) {
     os << " -> " << x.stmtFunction_->AsFortran();
   }
+  if (x.moduleInterface_) {
+    os << " moduleInterface: " << *x.moduleInterface_;
+  }
   return os;
 }
 
Index: flang/lib/Semantics/tools.cpp
===================================================================
--- flang/lib/Semantics/tools.cpp
+++ flang/lib/Semantics/tools.cpp
@@ -1058,14 +1058,9 @@
 
 const Symbol *FindSeparateModuleSubprogramInterface(const Symbol *proc) {
   if (proc) {
-    if (const Symbol * submodule{proc->owner().symbol()}) {
-      if (const auto *details{submodule->detailsIf<ModuleDetails>()}) {
-        if (const Scope * ancestor{details->ancestor()}) {
-          const Symbol *iface{ancestor->FindSymbol(proc->name())};
-          if (IsSeparateModuleProcedureInterface(iface)) {
-            return iface;
-          }
-        }
+    if (const auto *subprogram{proc->detailsIf<SubprogramDetails>()}) {
+      if (const Symbol * iface{subprogram->moduleInterface()}) {
+        return iface;
       }
     }
   }
Index: flang/test/Semantics/nullify02.f90
===================================================================
--- flang/test/Semantics/nullify02.f90
+++ flang/test/Semantics/nullify02.f90
@@ -34,7 +34,7 @@
 ! that has reported errors
 module badNullify
   interface
-    module function ptrFun()
+    function ptrFun()
       integer, pointer :: ptrFun
     end function
   end interface
Index: flang/test/Semantics/separate-mp02.f90
===================================================================
--- flang/test/Semantics/separate-mp02.f90
+++ flang/test/Semantics/separate-mp02.f90
@@ -149,9 +149,11 @@
   character(*), parameter :: suffix = "_xxx"
 contains
   !ERROR: Module subprogram 's1' has a binding label but the corresponding interface body does not
+  !ERROR: Module subprogram 's1' and its corresponding interface body are not both BIND(C)
   module subroutine s1() bind(c, name="s1")
   end
   !ERROR: Module subprogram 's2' does not have a binding label but the corresponding interface body does
+  !ERROR: Module subprogram 's2' and its corresponding interface body are not both BIND(C)
   module subroutine s2()
   end
   !ERROR: Module subprogram 's3' has binding label 's3_xxx' but the corresponding interface body has 's3'
Index: flang/test/Semantics/separate-mp03.f90
===================================================================
--- /dev/null
+++ flang/test/Semantics/separate-mp03.f90
@@ -0,0 +1,99 @@
+! RUN: %python %S/test_errors.py %s %flang_fc1
+! Tests module procedures declared and defined in the same module.
+
+! These cases are correct.
+module m1
+  interface
+    integer module function f1(x)
+      real, intent(in) :: x
+    end function
+    integer module function f2(x)
+      real, intent(in) :: x
+    end function
+    module function f3(x) result(res)
+      integer :: res
+      real, intent(in) :: x
+    end function
+    module function f4(x) result(res)
+      integer :: res
+      real, intent(in) :: x
+    end function
+    module subroutine s1
+    end subroutine
+    pure module subroutine s2
+    end subroutine
+    module subroutine s3
+    end subroutine
+  end interface
+ contains
+  integer module function f1(x)
+    real, intent(in) :: x
+    f1 = x
+  end function
+  module procedure f2
+    f2 = x
+  end procedure
+  module function f3(x) result(res)
+    integer :: res
+    real, intent(in) :: x
+    res = x
+  end function
+  module procedure f4
+    res = x
+  end procedure
+  module subroutine s1
+  end subroutine
+  pure module subroutine s2
+  end subroutine
+  module procedure s3
+  end procedure
+end module
+
+! Error cases
+
+module m2
+  interface
+    integer module function f1(x)
+      real, intent(in) :: x
+    end function
+    integer module function f2(x)
+      real, intent(in) :: x
+    end function
+    module function f3(x) result(res)
+      integer :: res
+      real, intent(in) :: x
+    end function
+    module function f4(x) result(res)
+      integer :: res
+      real, intent(in) :: x
+    end function
+    module subroutine s1
+    end subroutine
+    pure module subroutine s2
+    end subroutine
+  end interface
+ contains
+  integer module function f1(x)
+    !ERROR: Dummy argument 'x' has type INTEGER(4); the corresponding argument in the interface body has type REAL(4)
+    integer, intent(in) :: x
+    f1 = x
+  end function
+  !ERROR: 'notf2' was not declared a separate module procedure
+  module procedure notf2
+  end procedure
+  !ERROR: Return type of function 'f3' does not match return type of the corresponding interface body
+  module function f3(x) result(res)
+    real :: res
+    real, intent(in) :: x
+    res = x
+  end function
+  !ERROR: Module subroutine 'f4' was declared as a function in the corresponding interface body
+  module subroutine f4
+  end subroutine
+  !ERROR: Module function 's1' was declared as a subroutine in the corresponding interface body
+  module function s1
+  end function
+  !ERROR: Module subprogram 's2' and its corresponding interface body are not both PURE
+  impure module subroutine s2
+  end subroutine
+end module