diff --git a/math.c b/math.c
index 74dff9e720..523937ecb3 100644
--- a/math.c
+++ b/math.c
@@ -563,7 +563,7 @@ math_log10(VALUE unused_obj, VALUE x)
     /* check for pole error */
     if (d == 0.0) return DBL2NUM(-INFINITY);
 
-    return DBL2NUM(log10(d) + numbits * M_LN2/M_LN10); /* log10(d * 2 ** numbits) */
+    return DBL2NUM(log10(d) + numbits * log10(2)); /* log10(d * 2 ** numbits) */
 }
 
 /*