diff --git a/php-FIT-File-Analysis.php b/php-FIT-File-Analysis.php
index 334f01f..1a774c2 100644
--- a/php-FIT-File-Analysis.php
+++ b/php-FIT-File-Analysis.php
@@ -787,7 +787,8 @@ private function fix_data($options) {
 				$mesg_name = $this->data_mesg_info[$mesg['global_mesg_num']]['mesg_name'];
 				
 				foreach($mesg['field_defns'] as $field) {
-					if($field['base_type'] === 131) {  // Convert uint16 to sint16
+					// Convert uint16 to sint16
+					if($field['base_type'] === 131 && isset($this->data_mesg_info[$mesg['global_mesg_num']]['field_defns'][$field['field_definition_number']]['field_name'])) {
 						$field_name = $this->data_mesg_info[$mesg['global_mesg_num']]['field_defns'][$field['field_definition_number']]['field_name'];
 						if(is_array($this->data_mesgs[$mesg_name][$field_name])) {
 							foreach($this->data_mesgs[$mesg_name][$field_name] as &$v) {
@@ -800,7 +801,8 @@ private function fix_data($options) {
 							$this->data_mesgs[$mesg_name][$field_name] = -1 * ($this->data_mesgs[$mesg_name][$field_name] - 0x7FFF);
 						}
 					}
-					else if($field['base_type'] === 133) {  // Convert uint32 to sint32
+					// Convert uint32 to sint32
+					else if($field['base_type'] === 133 && isset($this->data_mesg_info[$mesg['global_mesg_num']]['field_defns'][$field['field_definition_number']]['field_name'])) {
 						$field_name = $this->data_mesg_info[$mesg['global_mesg_num']]['field_defns'][$field['field_definition_number']]['field_name'];
 						if(is_array($this->data_mesgs[$mesg_name][$field_name])) {
 							foreach($this->data_mesgs[$mesg_name][$field_name] as &$v) {
@@ -936,11 +938,13 @@ private function interpolate_missing_data(&$missing_keys, &$array){
 				if ($missing_keys[$i] > $max_key) {
 					$array[$missing_keys[$i]] = $array[$max_key];
 					continue;
-				} else if ($missing_keys[$i] < $max_key) {
+				} else if ($missing_keys[$i] < $min_key) {
 					$array[$missing_keys[$i]] = $array[$min_key];
 					continue;
 				}
 				
+				reset($array);
+				
 				while($missing_keys[$i] > key($array)) {
 					$prev_value = current($array);
 					next($array);