diff --git a/flang/lib/Optimizer/CodeGen/CodeGen.cpp b/flang/lib/Optimizer/CodeGen/CodeGen.cpp
--- a/flang/lib/Optimizer/CodeGen/CodeGen.cpp
+++ b/flang/lib/Optimizer/CodeGen/CodeGen.cpp
@@ -465,6 +465,20 @@
   }
 };
 
+/// Lower `fir.boxproc_host` operation. Extracts the host pointer from the
+/// boxproc.
+/// TODO: Part of supporting Fortran 2003 procedure pointers.
+struct BoxProcHostOpConversion : public FIROpConversion<fir::BoxProcHostOp> {
+  using FIROpConversion::FIROpConversion;
+
+  mlir::LogicalResult
+  matchAndRewrite(fir::BoxProcHostOp boxprochost, OpAdaptor adaptor,
+                  mlir::ConversionPatternRewriter &rewriter) const override {
+    return rewriter.notifyMatchFailure(
+        boxprochost, "fir.boxproc_host codegen is not implemented yet");
+  }
+};
+
 // `fir.call` -> `llvm.call`
 struct CallOpConversion : public FIROpConversion<fir::CallOp> {
   using FIROpConversion::FIROpConversion;
@@ -636,6 +650,19 @@
   }
 };
 
+/// Lower `fir.emboxproc` operation. Creates a procedure box.
+/// TODO: Part of supporting Fortran 2003 procedure pointers.
+struct EmboxProcOpConversion : public FIROpConversion<fir::EmboxProcOp> {
+  using FIROpConversion::FIROpConversion;
+
+  mlir::LogicalResult
+  matchAndRewrite(fir::EmboxProcOp emboxproc, OpAdaptor adaptor,
+                  mlir::ConversionPatternRewriter &rewriter) const override {
+    return rewriter.notifyMatchFailure(
+        emboxproc, "fir.emboxproc codegen is not implemented yet");
+  }
+};
+
 /// Lower `fir.has_value` operation to `llvm.return` operation.
 struct HasValueOpConversion : public FIROpConversion<fir::HasValueOp> {
   using FIROpConversion::FIROpConversion;
@@ -966,6 +993,20 @@
   }
 };
 
+/// Lower `fir.unboxproc` operation. Unbox a procedure box value, yielding its
+/// components.
+/// TODO: Part of supporting Fortran 2003 procedure pointers.
+struct UnboxProcOpConversion : public FIROpConversion<fir::UnboxProcOp> {
+  using FIROpConversion::FIROpConversion;
+
+  mlir::LogicalResult
+  matchAndRewrite(fir::UnboxProcOp unboxproc, OpAdaptor adaptor,
+                  mlir::ConversionPatternRewriter &rewriter) const override {
+    return rewriter.notifyMatchFailure(
+        unboxproc, "fir.unboxproc codegen is not implemented yet");
+  }
+};
+
 /// convert to LLVM IR dialect `undef`
 struct UndefOpConversion : public FIROpConversion<fir::UndefOp> {
   using FIROpConversion::FIROpConversion;
@@ -1414,14 +1455,15 @@
         AbsentOpConversion, AddcOpConversion, AddrOfOpConversion,
         AllocaOpConversion, BoxAddrOpConversion, BoxDimsOpConversion,
         BoxEleSizeOpConversion, BoxIsAllocOpConversion, BoxIsArrayOpConversion,
-        BoxIsPtrOpConversion, BoxRankOpConversion, CallOpConversion,
-        ConvertOpConversion, DispatchOpConversion, DispatchTableOpConversion,
-        DTEntryOpConversion, DivcOpConversion, ExtractValueOpConversion,
-        HasValueOpConversion, GlobalOpConversion, InsertOnRangeOpConversion,
-        InsertValueOpConversion, IsPresentOpConversion, LoadOpConversion,
-        NegcOpConversion, MulcOpConversion, SelectCaseOpConversion,
-        SelectOpConversion, SelectRankOpConversion, StoreOpConversion,
-        SubcOpConversion, UndefOpConversion, UnreachableOpConversion,
+        BoxIsPtrOpConversion, BoxProcHostOpConversion, BoxRankOpConversion,
+        CallOpConversion, ConvertOpConversion, DispatchOpConversion,
+        DispatchTableOpConversion, DTEntryOpConversion, DivcOpConversion,
+        EmboxProcOpConversion, ExtractValueOpConversion, HasValueOpConversion,
+        GlobalOpConversion, InsertOnRangeOpConversion, InsertValueOpConversion,
+        IsPresentOpConversion, LoadOpConversion, NegcOpConversion,
+        MulcOpConversion, SelectCaseOpConversion, SelectOpConversion,
+        SelectRankOpConversion, StoreOpConversion, SubcOpConversion,
+        UnboxProcOpConversion, UndefOpConversion, UnreachableOpConversion,
         ZeroOpConversion>(typeConverter);
     mlir::populateStdToLLVMConversionPatterns(typeConverter, pattern);
     mlir::arith::populateArithmeticToLLVMConversionPatterns(typeConverter,
diff --git a/flang/lib/Optimizer/CodeGen/TypeConverter.h b/flang/lib/Optimizer/CodeGen/TypeConverter.h
--- a/flang/lib/Optimizer/CodeGen/TypeConverter.h
+++ b/flang/lib/Optimizer/CodeGen/TypeConverter.h
@@ -54,6 +54,11 @@
       LLVM_DEBUG(llvm::dbgs() << "type convert: " << boxchar << '\n');
       return convertType(specifics->boxcharMemoryType(boxchar.getEleTy()));
     });
+    addConversion([&](BoxProcType boxproc) {
+      // TODO: Support for this type will be added later when the Fortran 2003
+      // procedure pointer feature is implemented.
+      return llvm::None;
+    });
     addConversion(
         [&](fir::CharacterType charTy) { return convertCharType(charTy); });
     addConversion([&](HeapType heap) { return convertPointerLike(heap); });
diff --git a/flang/test/Fir/convert-to-llvm-invalid.fir b/flang/test/Fir/convert-to-llvm-invalid.fir
--- a/flang/test/Fir/convert-to-llvm-invalid.fir
+++ b/flang/test/Fir/convert-to-llvm-invalid.fir
@@ -50,3 +50,49 @@
 ^bb3:
   return
 }
+
+// -----
+
+// Test that the type `fir.boxproc` fails to be legalized.
+// Not implemented yet.
+
+// expected-error@+1{{failed to legalize operation 'builtin.func'}}
+func private @foo0(%arg0: !fir.boxproc<() -> ()>)
+
+// -----
+
+// Test that `fir.emboxproc` fails to be legalized.
+// Not implemented yet.
+
+func private @method_impl(i32)
+
+func @emboxproc_test() {
+  %host_vars = fir.alloca tuple<i32,f64>
+// expected-error@+1{{failed to legalize operation 'fir.emboxproc'}}
+  %bproc = fir.emboxproc @method_impl, %host_vars : ((i32) -> (), !fir.ref<tuple<i32,f64>>) -> !fir.boxproc<(i32) -> ()>
+  return
+}
+
+// -----
+
+// Test that `fir.unboxproc` fails to be legalized.
+// Not implemented yet.
+
+func @unboxproc_test() {
+  %bproc = fir.call @get_bproc() : () -> (!fir.boxproc<(i32) -> ()>)
+// expected-error@+1{{failed to legalize operation 'fir.unboxproc'}}
+  %ubproc:2 = fir.unboxproc %bproc : (!fir.boxproc<(i32) -> ()>) -> ((i32) -> (), !fir.ref<tuple<i32,f64>>)
+  return
+}
+
+// -----
+
+// Test that `fir.boxproc_host` fails to be legalized.
+// Not implemented yet.
+
+func @boxproc_host_test() {
+  %bproc = fir.call @get_bproc() : () -> (!fir.boxproc<(i32) -> ()>)
+// expected-error@+1{{failed to legalize operation 'fir.boxproc_host'}}
+  %host_tuple = fir.boxproc_host %bproc : (!fir.boxproc<(i32) -> ()>) -> (!fir.ref<tuple<i32,f64>>)
+  return
+}