diff --git a/.travis.yml b/.travis.yml
index b79edcd..bebbc76 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -7,6 +7,7 @@ php:
   - 7.1
   - 7.2
   - 7.3
+  - 7.4
 
 cache:
   directories:
diff --git a/Spreadsheet/Excel/Writer/Parser.php b/Spreadsheet/Excel/Writer/Parser.php
index 9182f9b..0909969 100644
--- a/Spreadsheet/Excel/Writer/Parser.php
+++ b/Spreadsheet/Excel/Writer/Parser.php
@@ -1091,7 +1091,7 @@ protected function _cellToRowcol($cell)
         $col    = 0;
         $col_ref_length = strlen($col_ref);
         for ($i = 0; $i < $col_ref_length; $i++) {
-            $col += (ord($col_ref{$i}) - ord('A') + 1) * pow(26, $expn);
+            $col += (ord($col_ref[$i]) - ord('A') + 1) * pow(26, $expn);
             $expn--;
         }
 
@@ -1113,20 +1113,20 @@ protected function _advance()
         $formula_length = strlen($this->_formula);
         // eat up white spaces
         if ($i < $formula_length) {
-            while ($this->_formula{$i} == " ") {
+            while ($this->_formula[$i] == " ") {
                 $i++;
             }
 
             if ($i < ($formula_length - 1)) {
-                $this->_lookahead = $this->_formula{$i+1};
+                $this->_lookahead = $this->_formula[$i+1];
             }
             $token = '';
         }
 
         while ($i < $formula_length) {
-            $token .= $this->_formula{$i};
+            $token .= $this->_formula[$i];
             if ($i < ($formula_length - 1)) {
-                $this->_lookahead = $this->_formula{$i+1};
+                $this->_lookahead = $this->_formula[$i+1];
             } else {
                 $this->_lookahead = '';
             }
@@ -1141,7 +1141,7 @@ protected function _advance()
             }
 
             if ($i < ($formula_length - 2)) {
-                $this->_lookahead = $this->_formula{$i+2};
+                $this->_lookahead = $this->_formula[$i+2];
             } else { // if we run out of characters _lookahead becomes empty
                 $this->_lookahead = '';
             }
@@ -1292,7 +1292,7 @@ public function parse($formula)
     {
         $this->_current_char = 0;
         $this->_formula      = $formula;
-        $this->_lookahead    = $formula{1};
+        $this->_lookahead    = $formula[1];
         $this->_advance();
         $this->_parse_tree   = $this->_condition();
         if (PEAR::isError($this->_parse_tree)) {
diff --git a/Spreadsheet/Excel/Writer/Workbook.php b/Spreadsheet/Excel/Writer/Workbook.php
index 3c779ec..c4e66bf 100644
--- a/Spreadsheet/Excel/Writer/Workbook.php
+++ b/Spreadsheet/Excel/Writer/Workbook.php
@@ -1450,7 +1450,6 @@ protected function _calculateSharedStringsSizes()
          they must be written before the SST records
         */
 
-        $tmp_block_sizes = array();
         $tmp_block_sizes = $this->_block_sizes;
 
         $length  = 12;
diff --git a/composer.json b/composer.json
index 652509f..04869eb 100644
--- a/composer.json
+++ b/composer.json
@@ -52,7 +52,7 @@
     "require": {
         "pear/pear-core-minimal": "^1.10",
         "pear/ole": ">=1.0.0RC4",
-        "php": ">=5.3.3 <7.4"
+        "php": ">=5.3.3 <7.5"
     },
     "require-dev": {
         "phpunit/phpunit": "<6.0"