diff --git a/lslopt/lslbasefuncs.py b/lslopt/lslbasefuncs.py
index 71350ca..5668d74 100644
--- a/lslopt/lslbasefuncs.py
+++ b/lslopt/lslbasefuncs.py
@@ -1643,8 +1643,9 @@ def llRotBetween(v1, v2):
 
     ddc2 = dot*dot + csq
 
-    if ddc2 >= 1.5e-45:
-        if csq >= 1.5e-45:
+    DenormalStart = float.fromhex('0x1p-149')
+    if ddc2 >= DenormalStart:
+        if csq >= DenormalStart:
             s = math.sqrt(ddc2) + dot;
             m = math.sqrt(csq + s*s);
             return Quaternion(F32((cross[0]/m, cross[1]/m, cross[2]/m, s/m)))
@@ -1653,7 +1654,7 @@ def llRotBetween(v1, v2):
         if dot > 0:
             return ZERO_ROTATION
         m = math.sqrt(v1[0]*v1[0] + v1[1]*v1[1])
-        if m >= 1.5e-45:
+        if m >= DenormalStart:
             return Quaternion(F32((v1[1]/m, -v1[0]/m, 0., 0.)))
         return Quaternion((1., 0., 0., 0.))
     return ZERO_ROTATION