diff --git a/object.c b/object.c
index 4a5b5d359a..a4594a2982 100644
--- a/object.c
+++ b/object.c
@@ -3270,7 +3270,8 @@ rb_cstr_to_dbl_raise(const char *p, int badcheck, int raise, int *error)
     if (*end) {
         char buf[DBL_DIG * 4 + 10];
         char *n = buf;
-        char *e = buf + sizeof(buf) - 1;
+        char *const init_e = buf + DBL_DIG * 4;
+        char *e = init_e;
         char prev = 0;
 
         while (p < end && n < e) prev = *n++ = *p++;
@@ -3283,6 +3284,9 @@ rb_cstr_to_dbl_raise(const char *p, int badcheck, int raise, int *error)
                 }
             }
             prev = *p++;
+            if (e == init_e && (*p == 'e' || *p == 'E')) {
+                e = buf + sizeof(buf) - 1;
+            }
             if (n < e) *n++ = prev;
         }
         *n = '\0';
diff --git a/test/ruby/test_float.rb b/test/ruby/test_float.rb
index 24bed9269c..5686fd4617 100644
--- a/test/ruby/test_float.rb
+++ b/test/ruby/test_float.rb
@@ -163,6 +163,8 @@ class TestFloat < Test::Unit::TestCase
       assert_equal(-31.0*2**-1027, Float("-0x1f"+("0"*268)+".0p-2099"))
       assert_equal(-31.0*2**-1027, Float("-0x1f"+("0"*600)+".0p-3427"))
     end
+
+    assert_equal(1.0e10, Float("1.0_"+"00000"*Float::DIG+"e10"))
   end
 
   def test_divmod