diff --git a/ConflictSet.cpp b/ConflictSet.cpp
index c1ac8a6..e86bd37 100644
--- a/ConflictSet.cpp
+++ b/ConflictSet.cpp
@@ -578,7 +578,7 @@ int firstNonNeg1(const int8_t x[16]) {
   uint32_t bitfield = _mm_movemask_epi8(results) ^ 0xffff;
   if (bitfield == 0)
     return -1;
-  return __builtin_clz(bitfield);
+  return __builtin_ctz(bitfield);
 }
 
 int lastNonNeg1(const int8_t x[16]) {
@@ -589,7 +589,7 @@ int lastNonNeg1(const int8_t x[16]) {
   uint32_t bitfield = _mm_movemask_epi8(results) ^ 0xffff;
   if (bitfield == 0)
     return -1;
-  return 15 - __builtin_ctz(bitfield);
+  return 31 - __builtin_clz(bitfield);
 }
 #endif