diff --git a/flang/lib/Semantics/check-declarations.cpp b/flang/lib/Semantics/check-declarations.cpp
index a2f2906af10b8..c726be82eb313 100644
--- a/flang/lib/Semantics/check-declarations.cpp
+++ b/flang/lib/Semantics/check-declarations.cpp
@@ -66,6 +66,7 @@ class CheckHelper {
   void CheckVolatile(const Symbol &, const DerivedTypeSpec *);
   void CheckContiguous(const Symbol &);
   void CheckPointer(const Symbol &);
+  void CheckExternalAttrConflicts(const Symbol &);
   void CheckPassArg(
       const Symbol &proc, const Symbol *interface, const WithPassArg &);
   void CheckProcBinding(const Symbol &, const ProcBindingDetails &);
@@ -696,6 +697,8 @@ void CheckHelper::CheckObjectEntity(
   CheckConflicting(symbol, Attr::SAVE, Attr::PARAMETER);
   CheckConflicting(symbol, Attr::TARGET, Attr::PARAMETER);
   CheckConflicting(symbol, Attr::VOLATILE, Attr::PARAMETER);
+  CheckConflicting(symbol, Attr::EXTERNAL, Attr::PARAMETER);
+  CheckConflicting(symbol, Attr::INTRINSIC, Attr::PARAMETER);
   Check(details.shape());
   Check(details.coshape());
   if (details.shape().Rank() > common::maxRank) {
@@ -983,6 +986,7 @@ void CheckHelper::CheckObjectEntity(
     }
   }
   if (symbol.attrs().test(Attr::EXTERNAL)) {
+    CheckExternalAttrConflicts(symbol);
     SayWithDeclaration(symbol,
         "'%s' is a data object and may not be EXTERNAL"_err_en_US,
         symbol.name());
@@ -2460,6 +2464,10 @@ void CheckHelper::CheckPointer(const Symbol &symbol) { // C852
   }
 }
 
+void CheckHelper::CheckExternalAttrConflicts(const Symbol &symbol) {
+  CheckConflicting(symbol, Attr::EXTERNAL, Attr::INTRINSIC); // F'2023 C842
+}
+
 // C760 constraints on the passed-object dummy argument
 // C757 constraints on procedure pointer components
 void CheckHelper::CheckPassArg(
diff --git a/flang/test/Semantics/declarations02.f90 b/flang/test/Semantics/declarations02.f90
index 32c3517d13cd1..90f29f90d9d0e 100644
--- a/flang/test/Semantics/declarations02.f90
+++ b/flang/test/Semantics/declarations02.f90
@@ -24,6 +24,9 @@ module m
   target x4
   volatile x4
 
+  !ERROR: 'sin' may not have both the INTRINSIC and PARAMETER attributes
+  real, parameter, intrinsic :: sin
+
   type :: my_type1
     integer :: x4
   end type
diff --git a/flang/test/Semantics/declarations09.f90 b/flang/test/Semantics/declarations09.f90
new file mode 100644
index 0000000000000..8abe320f5d2f3
--- /dev/null
+++ b/flang/test/Semantics/declarations09.f90
@@ -0,0 +1,11 @@
+! RUN: %python %S/test_errors.py %s %flang_fc1 -pedantic
+
+subroutine bug149771
+
+  !ERROR: 'exp' may not have both the EXTERNAL and INTRINSIC attributes
+  real, external, intrinsic :: exp
+
+  !ERROR: 'x2' may not have both the EXTERNAL and PARAMETER attributes
+  integer, external, parameter :: x2
+
+end subroutine bug149771