diff -r cc0fc4e9b494 Python/dtoa.c
--- a/Python/dtoa.c	Sat Nov 23 21:14:42 2013 +0200
+++ b/Python/dtoa.c	Sat Nov 23 19:58:58 2013 +0000
@@ -207,6 +207,12 @@
 #define MAX_ABS_EXP 19999U
 #endif
 
+/* maximum permitted number of significant digits in the strtod input.
+   This should be chosen to safely fit into an int. */
+#ifndef MAX_SIGNIFICANT_DIGITS
+#define MAX_SIGNIFICANT_DIGITS 2000000000
+#endif
+
 /* The following definition of Storeinc is appropriate for MIPS processors.
  * An alternative that might be better on some machines is
  * #define Storeinc(a,b,c) (*a++ = b << 16 | c & 0xffff)
@@ -1538,6 +1544,7 @@
     Long L;
     BCinfo bc;
     Bigint *bb, *bb1, *bd, *bd0, *bs, *delta;
+    size_t pnd, pnd0;
 
     dval(&rv) = 0.;
 
@@ -1566,25 +1573,35 @@
     s0 = s1 = s;
     while ('0' <= c && c <= '9')
         c = *++s;
-    nd0 = nd = s - s1;
+    pnd0 = pnd = s - s1;
 
     /* Parse decimal point and following digits. */
     if (c == '.') {
         c = *++s;
-        if (!nd) {
+        if (!pnd) {
             s1 = s;
             while (c == '0')
                 c = *++s;
             lz = lz || s != s1;
-            nd0 -= s - s1;
+            pnd0 -= s - s1;
             s0 = s;
         }
         s1 = s;
         while ('0' <= c && c <= '9')
             c = *++s;
-        nd += s - s1;
+        pnd += s - s1;
     }
 
+    /* If there are more than MAX_SIGNIFICANT_DIGITS digits, report
+       a parse error. */
+    if (pnd > MAX_SIGNIFICANT_DIGITS) {
+        if (se)
+            *se = (char *)s00;
+        goto parse_error;
+    }
+    nd = (int)pnd;
+    nd0 = (int)pnd0;
+
     /* Now lz is true if and only if there were leading zero digits, and nd
        gives the total number of digits ignoring leading zeros.  A valid input
        must have at least one digit. */