diff --git a/exercises/practice/collatz-conjecture/.meta/example.s b/exercises/practice/collatz-conjecture/.meta/example.s
index e645852..5c622ad 100644
--- a/exercises/practice/collatz-conjecture/.meta/example.s
+++ b/exercises/practice/collatz-conjecture/.meta/example.s
@@ -1,3 +1,5 @@
+.equ INVALID_NUMBER, -1
+
 .text
 .globl steps
 
@@ -26,7 +28,7 @@ steps:
         b       .loop
 
 .invalid:
-        mov     x0, #-1
+        mov     x0, INVALID_NUMBER
 
 .return:
         ret
diff --git a/exercises/practice/collatz-conjecture/collatz_conjecture.s b/exercises/practice/collatz-conjecture/collatz_conjecture.s
index 58361be..cb56d32 100644
--- a/exercises/practice/collatz-conjecture/collatz_conjecture.s
+++ b/exercises/practice/collatz-conjecture/collatz_conjecture.s
@@ -1,3 +1,5 @@
+.equ INVALID_NUMBER, -1
+
 .text
 .globl steps
 
diff --git a/exercises/practice/collatz-conjecture/collatz_conjecture_test.c b/exercises/practice/collatz-conjecture/collatz_conjecture_test.c
index f90e0fe..5400dd6 100644
--- a/exercises/practice/collatz-conjecture/collatz_conjecture_test.c
+++ b/exercises/practice/collatz-conjecture/collatz_conjecture_test.c
@@ -2,7 +2,7 @@
 
 #include <stdint.h>
 
-#define ERROR_VALUE -1
+#define INVALID_NUMBER -1
 
 extern int steps(int64_t number);
 
@@ -33,12 +33,12 @@ void test_large_number_of_even_and_odd_steps(void) {
 
 void test_zero_is_an_error(void) {
     TEST_IGNORE();
-    TEST_ASSERT_EQUAL_INT(-1, steps(0));
+    TEST_ASSERT_EQUAL_INT(INVALID_NUMBER, steps(0));
 }
 
 void test_negative_value_is_an_error(void) {
     TEST_IGNORE();
-    TEST_ASSERT_EQUAL_INT(-1, steps(-15));
+    TEST_ASSERT_EQUAL_INT(INVALID_NUMBER, steps(-15));
 }
 
 void test_large_positive(void) {
@@ -48,7 +48,7 @@ void test_large_positive(void) {
 
 void test_large_negative(void) {
     TEST_IGNORE();
-    TEST_ASSERT_EQUAL_INT(-1, steps(-7001002003));
+    TEST_ASSERT_EQUAL_INT(INVALID_NUMBER, steps(-7001002003));
 }
 
 int main(void) {
diff --git a/generators/exercises/collatz_conjecture.py b/generators/exercises/collatz_conjecture.py
index e758489..bff5f1e 100644
--- a/generators/exercises/collatz_conjecture.py
+++ b/generators/exercises/collatz_conjecture.py
@@ -3,7 +3,7 @@
 
 #include <stdint.h>
 
-#define ERROR_VALUE -1
+#define INVALID_NUMBER -1
 
 extern int steps(int64_t number);
 """
@@ -33,5 +33,5 @@ def extra_cases():
 def gen_func_body(prop, inp, expected):
     number = inp["number"]
     if expected.__class__ == dict:
-        expected = -1
+        expected = 'INVALID_NUMBER'
     return f"TEST_ASSERT_EQUAL_INT({expected}, {prop}({number}));\n"