Index: flang/lib/Semantics/check-declarations.cpp
===================================================================
--- flang/lib/Semantics/check-declarations.cpp
+++ flang/lib/Semantics/check-declarations.cpp
@@ -115,6 +115,7 @@
   void CheckDioDummyIsScalar(const Symbol &, const Symbol &);
   void CheckDioDummyAttrs(const Symbol &, const Symbol &, Attr);
   void CheckDioDtvArg(const Symbol &, const Symbol *, GenericKind::DefinedIo);
+  void CheckGenericVsIntrinsic(const Symbol &, const GenericDetails &);
   void CheckDefaultIntegerArg(const Symbol &, const Symbol *, Attr);
   void CheckDioAssumedLenCharacterArg(
       const Symbol &, const Symbol *, std::size_t, Attr);
@@ -1148,6 +1149,11 @@
                  [&](const GenericKind::DefinedIo &io) {
                    CheckDefinedIoProc(symbol, details, io);
                  },
+                 [&](const GenericKind::OtherKind &other) {
+                   if (other == GenericKind::OtherKind::Name) {
+                     CheckGenericVsIntrinsic(symbol, details);
+                   }
+                 },
                  [](const auto &) {},
              },
       details.kind().u);
@@ -1941,6 +1947,40 @@
   }
 }
 
+// If an explicit INTRINSIC name is a function, so must all the specifics be,
+// and similarly for subroutines
+void CheckHelper::CheckGenericVsIntrinsic(
+    const Symbol &symbol, const GenericDetails &generic) {
+  if (symbol.attrs().test(Attr::INTRINSIC)) {
+    const evaluate::IntrinsicProcTable &table{
+        context_.foldingContext().intrinsics()};
+    bool isSubroutine{table.IsIntrinsicSubroutine(symbol.name().ToString())};
+    if (isSubroutine || table.IsIntrinsicFunction(symbol.name().ToString())) {
+      for (const SymbolRef &ref : generic.specificProcs()) {
+        const Symbol &ultimate{ref->GetUltimate()};
+        bool specificFunc{ultimate.test(Symbol::Flag::Function)};
+        bool specificSubr{ultimate.test(Symbol::Flag::Subroutine)};
+        if (!specificFunc && !specificSubr) {
+          if (const auto *proc{ultimate.detailsIf<SubprogramDetails>()}) {
+            if (proc->isFunction()) {
+              specificFunc = true;
+            } else {
+              specificSubr = true;
+            }
+          }
+        }
+        if ((specificFunc || specificSubr) &&
+            isSubroutine != specificSubr) { // C848
+          messages_.Say(symbol.name(),
+              "Generic interface '%s' with explicit intrinsic %s of the same name may not have specific procedure '%s' that is a %s"_err_en_US,
+              symbol.name(), isSubroutine ? "subroutine" : "function",
+              ref->name(), isSubroutine ? "function" : "subroutine");
+        }
+      }
+    }
+  }
+}
+
 void CheckHelper::CheckDefaultIntegerArg(
     const Symbol &subp, const Symbol *arg, Attr intent) {
   // Argument looks like: INTEGER, INTENT(intent) :: arg
Index: flang/lib/Semantics/expression.cpp
===================================================================
--- flang/lib/Semantics/expression.cpp
+++ flang/lib/Semantics/expression.cpp
@@ -2175,54 +2175,54 @@
     return std::nullopt; // also handles null symbol
   }
   const Symbol &ultimate{DEREF(symbol).GetUltimate()};
-  if (ultimate.attrs().test(semantics::Attr::INTRINSIC)) {
-    if (std::optional<SpecificCall> specificCall{context_.intrinsics().Probe(
-            CallCharacteristics{ultimate.name().ToString(), isSubroutine},
-            arguments, GetFoldingContext())}) {
-      CheckBadExplicitType(*specificCall, *symbol);
-      return CalleeAndArguments{
-          ProcedureDesignator{std::move(specificCall->specificIntrinsic)},
-          std::move(specificCall->arguments)};
-    }
-  } else {
-    CheckForBadRecursion(name.source, ultimate);
-    bool dueToNullActual{false};
-    if (ultimate.has<semantics::GenericDetails>()) {
-      ExpressionAnalyzer::AdjustActuals noAdjustment;
-      auto pair{ResolveGeneric(
-          *symbol, arguments, noAdjustment, mightBeStructureConstructor)};
-      symbol = pair.first;
-      dueToNullActual = pair.second;
-    }
-    if (symbol) {
-      if (symbol->GetUltimate().has<semantics::DerivedTypeDetails>()) {
-        if (mightBeStructureConstructor) {
-          return CalleeAndArguments{
-              semantics::SymbolRef{*symbol}, std::move(arguments)};
-        }
-      } else if (IsProcedure(*symbol)) {
+  CheckForBadRecursion(name.source, ultimate);
+  bool dueToNullActual{false};
+  bool isGenericInterface{ultimate.has<semantics::GenericDetails>()};
+  const Symbol *resolution{nullptr};
+  if (isGenericInterface) {
+    ExpressionAnalyzer::AdjustActuals noAdjustment;
+    auto pair{ResolveGeneric(
+        *symbol, arguments, noAdjustment, mightBeStructureConstructor)};
+    resolution = pair.first;
+    dueToNullActual = pair.second;
+  }
+  if (!resolution) {
+    // Not generic, or no resolution; may be intrinsic
+    if (!symbol->attrs().test(semantics::Attr::EXTERNAL)) {
+      if (std::optional<SpecificCall> specificCall{context_.intrinsics().Probe(
+              CallCharacteristics{ultimate.name().ToString(), isSubroutine},
+              arguments, GetFoldingContext())}) {
+        CheckBadExplicitType(*specificCall, *symbol);
         return CalleeAndArguments{
-            ProcedureDesignator{*symbol}, std::move(arguments)};
+            ProcedureDesignator{std::move(specificCall->specificIntrinsic)},
+            std::move(specificCall->arguments)};
+      } else if (symbol->attrs().test(semantics::Attr::INTRINSIC)) {
+        return std::nullopt;
       }
-      if (!context_.HasError(*symbol)) {
-        AttachDeclaration(
-            Say(name.source, "'%s' is not a callable procedure"_err_en_US,
-                name.source),
-            *symbol);
-      }
-    } else if (std::optional<SpecificCall> specificCall{
-                   context_.intrinsics().Probe(
-                       CallCharacteristics{
-                           ultimate.name().ToString(), isSubroutine},
-                       arguments, GetFoldingContext())}) {
-      // Generics can extend intrinsics
-      return CalleeAndArguments{
-          ProcedureDesignator{std::move(specificCall->specificIntrinsic)},
-          std::move(specificCall->arguments)};
+    }
+    if (isGenericInterface) {
+      EmitGenericResolutionError(*symbol, dueToNullActual);
+      return std::nullopt;
     } else {
-      EmitGenericResolutionError(*name.symbol, dueToNullActual);
+      // Neither a generic interface nor an intrinsic
+      resolution = symbol;
     }
   }
+  if (resolution->GetUltimate().has<semantics::DerivedTypeDetails>()) {
+    if (mightBeStructureConstructor) {
+      return CalleeAndArguments{
+          semantics::SymbolRef{*resolution}, std::move(arguments)};
+    }
+  } else if (IsProcedure(*resolution)) {
+    return CalleeAndArguments{
+        ProcedureDesignator{*resolution}, std::move(arguments)};
+  }
+  if (!context_.HasError(*resolution)) {
+    AttachDeclaration(
+        Say(name.source, "'%s' is not a callable procedure"_err_en_US,
+            name.source),
+        *resolution);
+  }
   return std::nullopt;
 }
 
Index: flang/lib/Semantics/resolve-names.cpp
===================================================================
--- flang/lib/Semantics/resolve-names.cpp
+++ flang/lib/Semantics/resolve-names.cpp
@@ -3809,7 +3809,9 @@
   HandleAttributeStmt(Attr::INTRINSIC, x.v);
   for (const auto &name : x.v) {
     auto &symbol{DEREF(FindSymbol(name))};
-    if (!ConvertToProcEntity(symbol)) {
+    if (symbol.has<GenericDetails>()) {
+      // Generic interface is extending intrinsic; ok
+    } else if (!ConvertToProcEntity(symbol)) {
       SayWithDecl(
           name, symbol, "INTRINSIC attribute not allowed on '%s'"_err_en_US);
     } else if (symbol.attrs().test(Attr::EXTERNAL)) { // C840
Index: flang/test/Semantics/resolve109.f90
===================================================================
--- /dev/null
+++ flang/test/Semantics/resolve109.f90
@@ -0,0 +1,58 @@
+! RUN: %python %S/test_errors.py %s %flang_fc1
+! Interfaces are allowed to extend intrinsic procedures, with limitations
+module m1
+  intrinsic sin
+  interface sin
+    module procedure :: charcpy
+  end interface
+  interface cos ! no INTRINSIC statement
+    module procedure :: charcpy
+  end interface
+  intrinsic mvbits
+  interface mvbits
+    module procedure :: negate
+  end interface
+  interface move_alloc ! no INTRINSIC statement
+    module procedure :: negate
+  end interface
+  interface tan ! not explicitly INTRINSIC
+    module procedure :: negate ! a subroutine
+  end interface
+  interface acos
+    module procedure :: minus ! override
+  end interface
+  intrinsic atan
+  !ERROR: Generic interface 'atan' with explicit intrinsic function of the same name may not have specific procedure 'negate' that is a subroutine
+  interface atan
+    module procedure :: negate ! a subroutine
+  end interface
+ contains
+  character function charcpy(x)
+    character, intent(in) :: x
+    charcpy = x
+  end function
+  subroutine negate(x)
+    real, intent(in out) :: x
+    x = -x
+  end subroutine
+  real elemental function minus(x)
+    real, intent(in) :: x
+    minus = -x
+  end function
+  subroutine test
+    integer, allocatable :: j, k
+    real :: x
+    character :: str
+    x = sin(x)
+    str = sin(str) ! charcpy
+    x = cos(x)
+    str = cos(str) ! charcpy
+    call mvbits(j,0,1,k,0)
+    call mvbits(x) ! negate
+    call move_alloc(j, k)
+    call move_alloc(x) ! negate
+    !ERROR: Cannot call subroutine 'tan' like a function
+    x = tan(x)
+    x = acos(x) ! user's interface overrides intrinsic
+  end subroutine
+end module