1 files changed, 1 insertions, 2 deletions
diff --git a/ext/bigdecimal/bigdecimal.c b/ext/bigdecimal/bigdecimal.c
index 298e73660f..4e124bdea1 100644
--- a/ext/bigdecimal/bigdecimal.c
+++ b/ext/bigdecimal/bigdecimal.c
@@ -2697,8 +2697,7 @@ rb_uint64_convert_to_BigDecimal(uint64_t uval, RB_UNUSED_VAR(size_t digs), int r
         vp->frac[0] = (DECDIG)uval;
     }
     else {
-        const size_t len10 = ceil(LOG10_2 * bit_length(uval));
-        size_t len = roomof(len10, BASE_FIG);
+        const size_t len = (size_t)ceil(log10(uval) / BASE_FIG);
 
         vp = VpAllocReal(len);
         vp->MaxPrec = len;