1 files changed, 16 insertions, 2 deletions

diff --git a/src/lib_string.c b/src/lib_string.c
index 1231aeb2..528b3d0e 100644
--- a/src/lib_string.c
+++ b/src/lib_string.c
@@ -734,9 +734,23 @@ LJLIB_CF(string_format)
         addintlen(form);
         sprintf(buff, form, (unsigned LUA_INTFRM_T)lj_lib_checknum(L, arg));
         break;
-      case 'e':  case 'E': case 'f': case 'g': case 'G':
-        sprintf(buff, form, (double)lj_lib_checknum(L, arg));
+      case 'e':  case 'E': case 'f': case 'g': case 'G': {
+        TValue tv;
+        tv.n = lj_lib_checknum(L, arg);
+        if (LJ_UNLIKELY((tv.u32.hi << 1) >= 0xffe00000)) {
+          /* Canonicalize output of non-finite values. */
+          size_t len = lj_str_bufnum(buff, &tv);
+          if (strfrmt[-1] == 'E' || strfrmt[-1] == 'G') {
+            buff[len-3] = buff[len-3] - 0x20;
+            buff[len-2] = buff[len-2] - 0x20;
+            buff[len-1] = buff[len-1] - 0x20;
+          }
+          luaL_addlstring(&b, buff, len);
+          continue;
+        }
+        sprintf(buff, form, (double)tv.n);
         break;
+        }
       case 'q':
         addquoted(L, &b, arg);
         continue;