diff --git a/bin/asl2c.py b/bin/asl2c.py
index 6e89e254..5c7af6d6 100755
--- a/bin/asl2c.py
+++ b/bin/asl2c.py
@@ -215,9 +215,13 @@ def report(x):
     if verbose:
         print(x)
 
+# Run command (printing command first if verbose) and abort if command fails
+# (The assumption is that the command printed a useful/meaningful error message already)
 def run(cmd):
     report(" ".join(cmd))
-    subprocess.run(cmd, check=True)
+    r = subprocess.run(cmd)
+    if r.returncode != 0:
+        exit(r.returncode)
 
 ################################################################
 # Compile/link flags
diff --git a/demo/Makefile b/demo/Makefile
index 0563e08b..8ea24a13 100644
--- a/demo/Makefile
+++ b/demo/Makefile
@@ -11,31 +11,50 @@ ASL_PATH = ..:.
 ASLI     = ../_build/default/bin/asli.exe
 ASL2C    = ../_build/default/bin/asl2c.py
 
+################################################################
+# Test whether we have GNU as or clang emulating as
+# (We can only build an elf file and run the test if we have
+# GNU as.)
+################################################################
+
+HAVE_GNU_AS := `as --version | grep -q 'GNU assembler'`
+
+REPORT_NOT_GAS = "Unable to build ELF file to use in demo: GNU 'as' required - skipping demo"
+
 ################################################################
 # Build a test program using the demo ISA
 ################################################################
 
 clean::
-	$(RM) test.s test.o test.elf
+	$(RM) test.o test.elf
 
-test.s : test.S assembly.s
+# run preprocessor on test.S using default rule
+test.s: test.S assembly.s
 
 test.o: test.s
-	as test.s -o test.o
+	@ if ${HAVE_GNU_AS}; then \
+	as test.s -o test.o; \
+	else echo ${REPORT_NOT_GAS}; fi
 
 test.elf: test.o
-	ld test.o -o test.elf
-	nm test.elf
+	@ if ${HAVE_GNU_AS}; then \
+	ld test.o -o test.elf; \
+	nm test.elf; \
+	else echo ${REPORT_NOT_GAS}; fi
 
 ################################################################
 # Run demo on interpreter
 ################################################################
 
 test: test.elf test.prj
-	env ASL_PATH="${ASL_PATH}" ${ASLI} --nobanner --batchmode demo.asl --project test.prj | filecheck test.prj
+	@ if ${HAVE_GNU_AS}; then \
+	env ASL_PATH="${ASL_PATH}" ${ASLI} --nobanner --batchmode demo.asl --project test.prj | filecheck test.prj ; \
+	else echo ${REPORT_NOT_GAS}; fi
 
 demo: test.elf
-	env ASL_PATH="${ASL_PATH}" ${ASLI} --batchmode demo.asl --project test.prj
+	@ if ${HAVE_GNU_AS}; then \
+	env ASL_PATH="${ASL_PATH}" ${ASLI} --batchmode demo.asl --project test.prj ; \
+	else echo ${REPORT_NOT_GAS}; fi
 
 ################################################################
 # Build simulator using C backend
@@ -52,15 +71,21 @@ CC=clang-16 -std=c2x
 .PRECIOUS: simulator_%
 
 simulator_% : simulator.c exports.json demo.asl
-	$(ASL2C) --basename=sim --intermediates=log --backend=$* > sim.prj
-	env ASL_PATH="${ASL_PATH}" $(ASLI) --nobanner --batchmode --project=sim.prj --configuration=exports.json demo.asl
-	$(CC) ${CFLAGS} simulator.c -o $@ ${LDFLAGS}
+	@ if ${HAVE_GNU_AS}; then \
+	$(ASL2C) --basename=sim --intermediates=log --backend=$* > sim.prj ; \
+	env ASL_PATH="${ASL_PATH}" $(ASLI) --nobanner --batchmode --project=sim.prj --configuration=exports.json demo.asl ; \
+	$(CC) ${CFLAGS} simulator.c -o $@ ${LDFLAGS} ; \
+	else echo ${REPORT_NOT_GAS}; fi
 
 test_% : simulator_% test.elf test.prj
-	./simulator_$* test.elf --steps=20 | filecheck test.prj
+	@ if ${HAVE_GNU_AS}; then \
+	./simulator_$* test.elf --steps=20 | filecheck test.prj ; \
+	else echo ${REPORT_NOT_GAS}; fi
 
 demo_% : simulator_% test.elf test.prj
-	./simulator_$* test.elf --steps=20
+	@ if ${HAVE_GNU_AS}; then \
+	./simulator_$* test.elf --steps=20; \
+	else echo ${REPORT_NOT_GAS}; fi
 
 clean ::
 	$(RM) sim.prj
diff --git a/runtime/.gitignore b/runtime/.gitignore
new file mode 100644
index 00000000..378eac25
--- /dev/null
+++ b/runtime/.gitignore
@@ -0,0 +1 @@
+build
diff --git a/runtime/lib/error.c b/runtime/lib/error.c
index 573cd3be..5a577973 100644
--- a/runtime/lib/error.c
+++ b/runtime/lib/error.c
@@ -20,14 +20,14 @@ extern "C" {
 void
 ASL_error(const char* loc, const char* msg)
 {
-        fprintf(stderr, "%s: ASL error: %s\n\n", loc, msg);
+        printf("%s: ASL error: %s\n\n", loc, msg);
         exit(1);
 }
 
 void
 ASL_runtime_error(const char *msg)
 {
-        fprintf(stderr, "Runtime error: %s\n", msg);
+        printf("Runtime error: %s\n", msg);
         exit(1);
 }
 
@@ -35,7 +35,7 @@ void
 ASL_assert(const char* loc, const char* expr, bool c)
 {
         if (!c) {
-                fprintf(stderr, "%s: Evaluation error: assertion failure: %s\n\n", loc, expr);
+                printf("%s: Evaluation error: assertion failure: %s\n\n", loc, expr);
                 exit(1);
         }
 }
diff --git a/tests/backends/stmt_assert_00.asl b/tests/backends/stmt_assert_00.asl
index b711c17d..e0306b39 100644
--- a/tests/backends/stmt_assert_00.asl
+++ b/tests/backends/stmt_assert_00.asl
@@ -1,4 +1,4 @@
-// RUN: not %aslrun %s |& filecheck %s
+// RUN: not %aslrun %s | filecheck %s
 // Copyright (C) 2023-2024 Intel Corporation
 
 func FUT(x : bits(4)) => bits(4)
diff --git a/tests/backends/stmt_case_01.asl b/tests/backends/stmt_case_01.asl
index 45e8f240..0b606eb6 100644
--- a/tests/backends/stmt_case_01.asl
+++ b/tests/backends/stmt_case_01.asl
@@ -1,4 +1,4 @@
-// RUN: not %aslrun %s |& filecheck %s
+// RUN: not %aslrun %s | filecheck %s
 // Copyright (C) 2023-2024 Intel Corporation
 
 func Test(x : integer) => integer
diff --git a/tests/backends/stmt_try_01.asl b/tests/backends/stmt_try_01.asl
index f05f9f0c..e90f051a 100644
--- a/tests/backends/stmt_try_01.asl
+++ b/tests/backends/stmt_try_01.asl
@@ -1,4 +1,4 @@
-// RUN: not %aslrun %s |& filecheck %s
+// RUN: not %aslrun %s | filecheck %s
 // Copyright (C) 2023-2024 Intel Corporation
 
 type E0 of exception;