diff --git a/include/graphblas/bsp1d/blas2.hpp b/include/graphblas/bsp1d/blas2.hpp
index e62c81971..c893accc5 100644
--- a/include/graphblas/bsp1d/blas2.hpp
+++ b/include/graphblas/bsp1d/blas2.hpp
@@ -90,6 +90,9 @@ namespace grb {
 				return SUCCESS;
 			}
 			if( descr & descriptors::dense ) {
+				if( nnz( u ) < size( u ) ) {
+					return ILLEGAL;
+				}
 				if( nnz( v ) < size( v ) ) {
 					return ILLEGAL;
 				}
@@ -233,6 +236,9 @@ namespace grb {
 				return SUCCESS;
 			}
 			if( descr & descriptors::dense ) {
+				if( nnz( u ) < size( u ) ) {
+					return ILLEGAL;
+				}
 				if( nnz( v ) < size( v ) ) {
 					return ILLEGAL;
 				}
diff --git a/include/graphblas/nonblocking/blas2.hpp b/include/graphblas/nonblocking/blas2.hpp
index 448f80a02..6981b62bd 100644
--- a/include/graphblas/nonblocking/blas2.hpp
+++ b/include/graphblas/nonblocking/blas2.hpp
@@ -499,6 +499,19 @@ namespace grb {
 				if( nnz( v ) < size( v ) ) {
 #ifdef _DEBUG
 					std::cout << "\t Dense descriptor given but input vector was sparse\n";
+#endif
+					return ILLEGAL;
+				}
+				if( nnz( u ) < size( u ) ) {
+#ifdef _DEBUG
+					std::cout << "\t Dense descriptor given but output vector was sparse\n";
+#endif
+					return ILLEGAL;
+				}
+				if( size( mask ) > 0 && nnz( mask ) < size( mask ) ) {
+#ifdef _DEBUG
+					std::cout << "\t Dense descriptor given but output mask has sparse "
+						<< "structure\n";
 #endif
 					return ILLEGAL;
 				}
diff --git a/include/graphblas/reference/blas2.hpp b/include/graphblas/reference/blas2.hpp
index 7a4d3e135..cd8931014 100644
--- a/include/graphblas/reference/blas2.hpp
+++ b/include/graphblas/reference/blas2.hpp
@@ -951,6 +951,12 @@ namespace grb {
 				if( nnz( v ) < size( v ) ) {
 #ifdef _DEBUG
 					std::cout << "\t Dense descriptor given but input vector was sparse\n";
+#endif
+					return ILLEGAL;
+				}
+				if( nnz( u ) < size( u ) ) {
+#ifdef _DEBUG
+					std::cout << "\t Dense descriptor given but output vector was sparse\n";
 #endif
 					return ILLEGAL;
 				}
diff --git a/tests/unit/CMakeLists.txt b/tests/unit/CMakeLists.txt
index 5cd03cf77..40302ee5d 100644
--- a/tests/unit/CMakeLists.txt
+++ b/tests/unit/CMakeLists.txt
@@ -272,6 +272,10 @@ add_grb_executables( dense_spmv dense_spmv.cpp
 	BACKENDS reference reference_omp bsp1d hybrid hyperdags nonblocking
 )
 
+add_grb_executables( illegal_spmv illegal_spmv.cpp
+	BACKENDS reference reference_omp bsp1d hybrid hyperdags nonblocking
+)
+
 add_grb_executables( moveMatrix moveMatrix.cpp
 	BACKENDS reference reference_omp bsp1d hybrid hyperdags nonblocking
 )
diff --git a/tests/unit/illegal_spmv.cpp b/tests/unit/illegal_spmv.cpp
new file mode 100644
index 000000000..d0d0823ca
--- /dev/null
+++ b/tests/unit/illegal_spmv.cpp
@@ -0,0 +1,180 @@
+
+/*
+ *   Copyright 2021 Huawei Technologies Co., Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <iostream>
+#include <sstream>
+
+#include <graphblas.hpp>
+
+bool exec_tests(
+	const grb::Matrix< void > &A, const grb::Matrix< char > &B,
+	grb::Vector< bool > &out, grb::Vector< bool > &out2,
+	const grb::Vector< char > &in, const grb::Vector< char > &in2,
+	const size_t offset
+) {
+	grb::semirings::boolean ring;
+
+	// at least one of the vectors is sparse
+	assert(
+			grb::nnz( out ) < grb::size( out ) ||
+			grb::nnz( out2 ) < grb::size( out2 ) ||
+			grb::nnz( in ) < grb::size( in ) ||
+			grb::nnz( in2 ) < grb::size( in2 )
+		  );
+
+	// test 1, exec
+	grb::RC rc = grb::mxv< grb::descriptors::dense >( out, A, in2, ring );
+	if( rc != grb::ILLEGAL ) {
+		std::cerr << "\t test " << offset << " FAILED\n";
+		return false;
+	}
+
+	// test 2, exec
+	rc = grb::vxm< grb::descriptors::dense >( out2, in, A, ring );
+	if( rc != grb::ILLEGAL ) {
+		std::cerr << "\t test " << (1 + offset) << " FAILED\n";
+		return false;
+	}
+
+	// test 3, exec
+	rc = grb::mxv< grb::descriptors::dense >( out2, B, in, ring );
+	if( rc != grb::ILLEGAL ) {
+		std::cerr << "\t test " << (2 + offset) << " FAILED\n";
+		return false;
+	}
+
+	// test 4, exec
+	rc = grb::vxm< grb::descriptors::dense >( out, in2, B, ring );
+	if( rc != grb::ILLEGAL ) {
+		std::cerr << "\t test " << (3 + offset) << " FAILED\n";
+		return false;
+	}
+
+	return true;
+}
+
+void grb_program( const size_t &n, grb::RC &rc ) {
+
+	// repeatedly used containers
+	grb::Matrix< void > A( n, 2 * n );
+	grb::Matrix< char > B( 2 * n, n );
+	grb::Vector< bool > out( n ), out2( 2 * n );
+	grb::Vector< char > in( n ), in2( 2 * n );
+
+	// run tests 1-4
+	if( !exec_tests( A, B, out, out2, in, in2, 1 ) ) {
+		rc = grb::FAILED;
+		return;
+	}
+
+	// init tests 5-8
+	rc = grb::setElement( out, true, 0 );
+	rc = rc ? rc : grb::setElement( out2, true, 0 );
+	if( rc != grb::SUCCESS ) {
+		std::cout << "Test batch 5-8: initialisation FAILED\n";
+		return;
+	}
+
+	// run tests 5-8
+	if( !exec_tests( A, B, out, out2, in, in2, 5 ) ) {
+		rc = grb::FAILED;
+		return;
+	}
+
+	// init tests 9-12
+	rc = grb::set( in, 1 );
+	rc = rc ? rc : grb::set( in2, 1 );
+	rc = rc ? rc : grb::setElement( in, 0, n - 1 );
+	rc = rc ? rc : grb::setElement( in2, 0, 2 * n - 1 );
+	rc = rc ? rc : grb::set( out, in, false );
+	rc = rc ? rc : grb::set( out2, in2, false );
+	if( rc != grb::SUCCESS ) {
+		std::cout << "Test batch 9-12: initialisation FAILED\n";
+		return;
+	}
+	
+	// run tests 9-12
+	if( !exec_tests( A, B, out, out2, in, in2, 9 ) ) {
+		rc = grb::FAILED;
+		return;
+	}
+
+	// init tests 13-16
+	rc = rc ? rc : grb::set( in, out, 2 );
+	rc = rc ? rc : grb::set( in2, out2, 3 );
+	rc = rc ? rc : grb::set( out, true );
+	rc = rc ? rc : grb::set( out2, true );
+	if( rc != grb::SUCCESS ) {
+		std::cout << "Test batch 13-16: initialisation FAILED\n";
+		return;
+	}
+
+	// run tests 13-16
+	if( !exec_tests( A, B, out, out2, in, in2, 13 ) ) {
+		rc = grb::FAILED;
+		return;
+	}
+}
+
+int main( int argc, char ** argv ) {
+	// defaults
+	bool printUsage = false;
+	size_t in = 100;
+
+	// error checking
+	if( argc > 2 ) {
+		printUsage = true;
+	}
+	if( argc == 2 ) {
+		size_t read;
+		std::istringstream ss( argv[ 1 ] );
+		if( ! ( ss >> read ) ) {
+			std::cerr << "Error parsing first argument\n";
+			printUsage = true;
+		} else if( ! ss.eof() ) {
+			std::cerr << "Error parsing first argument\n";
+			printUsage = true;
+		} else if( read % 2 != 0 ) {
+			std::cerr << "Given value for n is odd\n";
+			printUsage = true;
+		} else {
+			// all OK
+			in = read;
+		}
+	}
+	if( printUsage ) {
+		std::cerr << "Usage: " << argv[ 0 ] << " [n]\n";
+		std::cerr << "  -n (optional, default is 100): an even integer, the "
+		             "test size.\n";
+		return 1;
+	}
+
+	std::cout << "This is functional test " << argv[ 0 ] << "\n";
+	grb::Launcher< grb::AUTOMATIC > launcher;
+	grb::RC out;
+	if( launcher.exec( &grb_program, in, out, true ) != grb::SUCCESS ) {
+		std::cerr << "Launching test FAILED\n";
+		return 255;
+	}
+	if( out != grb::SUCCESS ) {
+		std::cerr << "Test FAILED (" << grb::toString( out ) << ")" << std::endl;
+	} else {
+		std::cout << "Test OK" << std::endl;
+	}
+	return 0;
+}
+
diff --git a/tests/unit/unittests.sh b/tests/unit/unittests.sh
index 0b49d2421..70cb92dea 100755
--- a/tests/unit/unittests.sh
+++ b/tests/unit/unittests.sh
@@ -607,6 +607,20 @@ for MODE in ${MODES}; do
 				fi
 				echo " "
 
+				echo ">>>      [x]           [ ]       Testing matrix times vector using at least one sparse"
+				echo "                                 vector while the dense descriptor is set"
+				$runner ${TEST_BIN_DIR}/illegal_spmv_${MODE}_${BACKEND} &> ${TEST_OUT_DIR}/illegal_spmv_${MODE}_${BACKEND}_${P}_${T}.log
+				head -1 ${TEST_OUT_DIR}/illegal_spmv_${MODE}_${BACKEND}_${P}_${T}.log
+				grep -i 'Test OK' ${TEST_OUT_DIR}/illegal_spmv_${MODE}_${BACKEND}_${P}_${T}.log || echo "Test FAILED"
+				echo " "
+
+				echo ">>>      [x]           [ ]       Testing matrix times vector using at least one sparse"
+				echo "                                 vector while the dense descriptor is set (large vectors)"
+				$runner ${TEST_BIN_DIR}/illegal_spmv_${MODE}_${BACKEND} 100000 &> ${TEST_OUT_DIR}/illegal_spmv_large_${MODE}_${BACKEND}_${P}_${T}.log
+				head -1 ${TEST_OUT_DIR}/illegal_spmv_large_${MODE}_${BACKEND}_${P}_${T}.log
+				grep -i 'Test OK' ${TEST_OUT_DIR}/illegal_spmv_large_${MODE}_${BACKEND}_${P}_${T}.log || echo "Test FAILED"
+				echo " "
+
 				echo ">>>      [x]           [ ]       Testing matrix times dense vector using the double (+,*)"
 				echo "                                 semiring where matrix elements are doubles and vector"
 				echo "                                 elements ints. The input matrix is taken from west0497."