diff --git a/src/system/libroot/posix/glibc/stdlib/strtod.c b/src/system/libroot/posix/glibc/stdlib/strtod.c
index 85642b89cf..b5d82692ab 100644
--- a/src/system/libroot/posix/glibc/stdlib/strtod.c
+++ b/src/system/libroot/posix/glibc/stdlib/strtod.c
@@ -674,18 +674,29 @@ INTERNAL (STRTOF) (nptr, endptr, group LOCALE_PARAM)
 
   /* If no other digit but a '0' is found the result is 0.0.
      Return current read pointer.  */
-  if ((c < L_('0') || c > L_('9'))
-      && (base == 16 && (c < TOLOWER (L_('a')) || c > TOLOWER (L_('f'))))
+  if (!((c >= L_('0') && c <= L_('9'))
+	|| (base == 16 && ((CHAR_TYPE) TOLOWER (c) >= L_('a')
+			   && (CHAR_TYPE) TOLOWER (c) <= L_('f')))
+	|| (
 #ifdef USE_WIDE_CHAR
-      && c != decimal
+	    c == (wint_t) decimal
 #else
-      && ({ for (cnt = 0; decimal[cnt] != '\0'; ++cnt)
-	      if (decimal[cnt] != cp[cnt])
-		break;
-	    decimal[cnt] != '\0'; })
+	    ({ for (cnt = 0; decimal[cnt] != '\0'; ++cnt)
+		 if (decimal[cnt] != cp[cnt])
+		   break;
+	       decimal[cnt] == '\0'; })
 #endif
-      && (base == 16 && (cp == start_of_digits || TOLOWER (c) != L_('p')))
-      && (base != 16 && TOLOWER (c) != L_('e')))
+	    /* '0x.' alone is not a valid hexadecimal number.
+	       '.' alone is not valid either, but that has been checked
+	       already earlier.  */
+	    && (base != 16
+		|| cp != start_of_digits
+		|| (cp[decimal_len] >= L_('0') && cp[decimal_len] <= L_('9'))
+		|| ((CHAR_TYPE) TOLOWER (cp[decimal_len]) >= L_('a')
+		    && (CHAR_TYPE) TOLOWER (cp[decimal_len]) <= L_('f'))))
+	|| (base == 16 && (cp != start_of_digits
+			   && (CHAR_TYPE) TOLOWER (c) == L_('p')))
+	|| (base != 16 && (CHAR_TYPE) TOLOWER (c) == L_('e'))))
     {
       tp = correctly_grouped_prefix (start_of_digits, cp, thousands, grouping);
       /* If TP is at the start of the digits, there was no correctly