diff --git a/c-print-fibonacci/Makefile b/c-print-fibonacci/Makefile
new file mode 100644
index 0000000..49d1aab
--- /dev/null
+++ b/c-print-fibonacci/Makefile
@@ -0,0 +1 @@
+include ../common/common.mk
diff --git a/c-print-fibonacci/main.c b/c-print-fibonacci/main.c
new file mode 100644
index 0000000..6cd2b4c
--- /dev/null
+++ b/c-print-fibonacci/main.c
@@ -0,0 +1,49 @@
+static void putc(int);
+static void puti(int);
+static int fib(int);
+
+/* TODO: this sample fails to compile on higher -O values */
+
+void _start(void)
+{
+	asm volatile ("law 04000");
+	asm volatile ("dac 209");
+	asm volatile ("law 03000");
+	asm volatile ("dac 208");
+
+	int n;
+
+	for (int i = 0; i < 20; i++) {
+		puti(fib(i));
+		putc(033);
+	}
+
+	asm volatile ("hlt");
+	__builtin_unreachable();
+}
+
+static void putc(int c)
+{
+	asm volatile ("lio %0" : : "r"(c) : "io");
+	asm volatile ("tyo");
+}
+
+/* TODO: this is printing out digits in reverse order; fix it */
+static void puti(int i)
+{
+	int mod;
+
+	do {
+		mod = i % 10;
+		putc((mod == 0) ? 020 : mod);
+		i /= 10;
+	} while (i != 0);
+}
+
+static int fib(int n)
+{
+	if (n <= 1)
+		return n;
+	else
+		return fib(n - 1) + fib(n - 2);
+}
diff --git a/common/common.mk b/common/common.mk
index 8fb7202..1132be7 100644
--- a/common/common.mk
+++ b/common/common.mk
@@ -1,4 +1,5 @@
 APP_NAME ?=	main
+CCFLAGS ?=	-O0
 objects-asm :=	$(patsubst %.S,%.o,$(wildcard *.S)) 
 objects-c :=	$(patsubst %.c,%.o,$(wildcard *.c)) 
 objects :=	$(objects-asm) $(objects-c)
@@ -6,7 +7,7 @@ objects :=	$(objects-asm) $(objects-c)
 default: $(APP_NAME).rim
 
 %.s: %.c
-	../build-gcc/gcc/cc1 $<
+	../build-gcc/gcc/cc1 $(CCFLAGS) $<
 
 %.o: %.S
 	pdp1-elf-as $< -o $@
diff --git a/tests/test.exp b/tests/test.exp
index f41adad..44126ab 100644
--- a/tests/test.exp
+++ b/tests/test.exp
@@ -2,6 +2,7 @@ set timeout 1
 
 proc run_test { demo_name expected_output } {
 	spawn "pdp1"
+	send "set cpu mdv\n"
 	send "attach ptr $demo_name/main.rim\n"
 	expect {
 		"PTR: creating new file"	{ fail "$demo_name: Didn't find the RIM tape file\n" }
@@ -31,3 +32,4 @@ run_test "c-print-for-loop" "xxxxyxxx"
 run_test "c-test-comparison" "aceg"
 run_test "c-test-arith" "xx"
 run_test "c-test-recursion" "xxxxxxxxxxxxxxxxxxxx"
+run_test "c-print-fibonacci" "0,1,1,2,3,5,8,31,12,43,55,98,441,332,773,016,789,7951,4852,1814,"