diff --git a/ext/standard/file.c b/ext/standard/file.c
index d51a584ed9c7a..8bab36096b1cf 100644
--- a/ext/standard/file.c
+++ b/ext/standard/file.c
@@ -834,7 +834,7 @@ PHP_FUNCTION(tempnam)
 	ZEND_PARSE_PARAMETERS_END();
 
 	p = php_basename(prefix, prefix_len, NULL, 0);
-	if (ZSTR_LEN(p) > 64) {
+	if (ZSTR_LEN(p) >= 64) {
 		ZSTR_VAL(p)[63] = '\0';
 	}
 
diff --git a/ext/standard/tests/file/tempnam_variation9.phpt b/ext/standard/tests/file/tempnam_variation9.phpt
new file mode 100644
index 0000000000000..9ccff1fca8980
--- /dev/null
+++ b/ext/standard/tests/file/tempnam_variation9.phpt
@@ -0,0 +1,76 @@
+--TEST--
+Test tempnam() function: usage variations - test prefix maximum size
+--SKIPIF--
+<?php
+if(substr(PHP_OS, 0, 3) == "WIN")
+  die("skip Do not run on Windows");
+?>
+--FILE--
+<?php
+/* Testing the maximum prefix size */
+
+echo "*** Testing tempnam() maximum prefix size ***\n";
+$file_path = __DIR__."/tempnamVar9";
+mkdir($file_path);
+
+$pre_prefix = "begin_";
+$post_prefix = "_end";
+$fixed_length = strlen($pre_prefix) + strlen($post_prefix);
+/* An array of prefixes */
+$names_arr = array(
+  $pre_prefix . str_repeat("x", 7) . $post_prefix,
+  $pre_prefix . str_repeat("x", 63 - $fixed_length) . $post_prefix,
+  $pre_prefix . str_repeat("x", 64 - $fixed_length) . $post_prefix,
+  $pre_prefix . str_repeat("x", 65 - $fixed_length) . $post_prefix,
+  $pre_prefix . str_repeat("x", 300) . $post_prefix,
+);
+
+foreach($names_arr as $i=>$prefix) {
+  echo "-- Iteration $i --\n";
+  try {
+    $file_name = tempnam("$file_path", $prefix);
+  } catch (Error $e) {
+    echo $e->getMessage(), "\n";
+    continue;
+  }
+
+  $base_name = basename($file_name);
+  echo "File name is => ";
+  print($base_name);
+  echo "\n";
+  echo "File name length is => ";
+  print(strlen($base_name));
+  echo "\n";
+
+  if (file_exists($file_name)) {
+    unlink($file_name);
+  }
+}
+rmdir($file_path);
+
+?>
+--CLEAN--
+<?php
+$file_path = __DIR__."/tempnamVar9";
+if (file_exists($file_path)) {
+    array_map('unlink', glob($file_path . "/*"));
+    rmdir($file_path);
+}
+?>
+--EXPECTF--
+*** Testing tempnam() maximum prefix size ***
+-- Iteration 0 --
+File name is => begin_%rx{7}%r_end%r.{6}%r
+File name length is => 23
+-- Iteration 1 --
+File name is => begin_%rx{53}%r_end%r.{6}%r
+File name length is => 69
+-- Iteration 2 --
+File name is => begin_%rx{54}%r_en%r.{6}%r
+File name length is => 69
+-- Iteration 3 --
+File name is => begin_%rx{55}%r_e%r.{6}%r
+File name length is => 69
+-- Iteration 4 --
+File name is => begin_%rx{57}%r%r.{6}%r
+File name length is => 69