diff --git a/plugins/sources/spreadsheet.inc b/plugins/sources/spreadsheet.inc
index d25692f..b7b6de7 100644
--- a/plugins/sources/spreadsheet.inc
+++ b/plugins/sources/spreadsheet.inc
@@ -25,6 +25,13 @@ class MigrateSourceSpreadsheet extends MigrateSource {
   protected $workbook;
 
   /**
+   * PHPExcel object for storing the worksheet data.
+   *
+   * @var PHPExcel_Worksheet
+   */
+  protected $worksheet;
+
+  /**
    * The name of the worksheet that will be processed.
    *
    * @var string
@@ -76,15 +83,13 @@ class MigrateSourceSpreadsheet extends MigrateSource {
 
     // Load the workbook.
     if ($this->load()) {
-      $worksheet = $this->workbook->getSheet();
-
       // Get the dimensions of the worksheet.
-      $this->rows = $worksheet->getHighestDataRow();
-      $this->cols = PHPExcel_Cell::columnIndexFromString($worksheet->getHighestDataColumn());
+      $this->rows = $this->worksheet->getHighestDataRow();
+      $this->cols = PHPExcel_Cell::columnIndexFromString($this->worksheet->getHighestDataColumn());
 
       // Map field names to their column index.
       for ($col = 0; $col < $this->cols; ++$col) {
-        $this->fields[$col] = trim($worksheet->getCellByColumnAndRow($col, 1)->getValue());
+        $this->fields[$col] = trim($this->worksheet->getCellByColumnAndRow($col, 1)->getValue());
       }
 
       $this->unload();
@@ -128,6 +133,7 @@ class MigrateSourceSpreadsheet extends MigrateSource {
       $reader->setLoadSheetsOnly($this->sheetName);
       // Load the source file.
       $this->workbook = $reader->load($this->file);
+      $this->worksheet = $this->workbook->getSheet();
     }
     catch (Exception $e) {
       Migration::displayMessage(t('Error loading file: %message', array('%message' => $e->getMessage())));
@@ -199,14 +205,17 @@ class MigrateSourceSpreadsheet extends MigrateSource {
    * @return null|object
    */
   public function getNextRow() {
+    migrate_instrument_start('MigrateSourceSpreadsheet::next');
     ++$this->rowNumber;
 
+    $source_keys = array_keys($this->activeMap->getSourceKey());
+
     if ($this->rowNumber <= $this->rows) {
-      $worksheet = $this->workbook->getSheet();
       $row_values = array();
-
       for ($col = 0; $col < $this->cols; ++$col) {
-        $row_values[$this->fields[$col]] = trim($worksheet->getCellByColumnAndRow($col, $this->rowNumber)->getValue());
+        if (in_array($this->fields[$col], $source_keys)) {
+          $row_values[$this->fields[$col]] = trim($this->worksheet->getCellByColumnAndRow($col, $this->rowNumber)->getValue());
+        }
       }
 
       return (object) $row_values;
@@ -214,7 +223,10 @@ class MigrateSourceSpreadsheet extends MigrateSource {
     else {
       // EOF, close the workbook.
       $this->unload();
+
+      migrate_instrument_stop('MigrateSourceSpreadsheet::next');
       return NULL;
     }
   }
+
 }