--- a/tests/cxxrtl/run-test.sh
+++ b/tests/cxxrtl/run-test.sh
@@ -5,7 +5,7 @@ set -ex
 run_subtest () {
     local subtest=$1; shift
 
-    ${CC:-gcc} -std=c++11 -O2 -o cxxrtl-test-${subtest} -I../../backends/cxxrtl/runtime test_${subtest}.cc -lstdc++
+    ${CXX:-gcc} -std=c++11 -O2 -o cxxrtl-test-${subtest} -I../../backends/cxxrtl/runtime test_${subtest}.cc -lstdc++
     ./cxxrtl-test-${subtest}
 }
 
@@ -14,4 +14,4 @@ run_subtest value_fuzz
 
 # Compile-only test.
 ../../yosys -p "read_verilog test_unconnected_output.v; proc; clean; write_cxxrtl cxxrtl-test-unconnected_output.cc"
-${CC:-gcc} -std=c++11 -c -o cxxrtl-test-unconnected_output -I../../backends/cxxrtl/runtime cxxrtl-test-unconnected_output.cc
+${CXX:-gcc} -std=c++11 -c -o cxxrtl-test-unconnected_output -I../../backends/cxxrtl/runtime cxxrtl-test-unconnected_output.cc
diff --git a/tests/fmt/run-test.sh b/tests/fmt/run-test.sh
index 998047f83..2a4a59f01 100644
--- a/tests/fmt/run-test.sh
+++ b/tests/fmt/run-test.sh
@@ -51,7 +51,7 @@ test_cxxrtl () {
 	local subtest=$1; shift
 
 	../../yosys -p "read_verilog ${subtest}.v; proc; clean; write_cxxrtl -print-output std::cerr yosys-${subtest}.cc"
-	${CC:-gcc} -std=c++11 -o yosys-${subtest} -I../../backends/cxxrtl/runtime ${subtest}_tb.cc -lstdc++
+	${CXX:-gcc} -std=c++11 -o yosys-${subtest} -I../../backends/cxxrtl/runtime ${subtest}_tb.cc -lstdc++
 	./yosys-${subtest} 2>yosys-${subtest}.log
 	iverilog -o iverilog-${subtest} ${subtest}.v ${subtest}_tb.v
 	./iverilog-${subtest} |grep -v '\$finish called' >iverilog-${subtest}.log
@@ -69,7 +69,7 @@ diff iverilog-always_full.log iverilog-always_full-1.log
 
 ../../yosys -p "read_verilog display_lm.v" >yosys-display_lm.log
 ../../yosys -p "read_verilog display_lm.v; write_cxxrtl yosys-display_lm.cc"
-${CC:-gcc} -std=c++11 -o yosys-display_lm_cc -I../../backends/cxxrtl/runtime display_lm_tb.cc -lstdc++
+${CXX:-gcc} -std=c++11 -o yosys-display_lm_cc -I../../backends/cxxrtl/runtime display_lm_tb.cc -lstdc++
 ./yosys-display_lm_cc >yosys-display_lm_cc.log
 for log in yosys-display_lm.log yosys-display_lm_cc.log; do
 	grep "^%l: \\\\bot\$" "$log"