diff --git a/inc/inc.ClassConversionServiceExec.php b/inc/inc.ClassConversionServiceExec.php
index b16ec08c3..bf973b6c6 100644
--- a/inc/inc.ClassConversionServiceExec.php
+++ b/inc/inc.ClassConversionServiceExec.php
@@ -159,6 +159,7 @@ class SeedDMS_ConversionServiceExec extends SeedDMS_ConversionServiceBase {
 		/* %s was just added because the commands to convert to text/plain used
 		 * it instead of %f for the input file
 		 * %f = input file
+		 * %if = format (jpg, png, pdf, gif)
 		 * %o = output file
 		 * %m = mime type
 		 * %w = width
@@ -175,6 +176,12 @@ class SeedDMS_ConversionServiceExec extends SeedDMS_ConversionServiceBase {
 			}
 			return false;
 		}
+		if(!empty($ret['stderr'])) {
+			if($this->logger) {
+				$this->logger->log('Conversion from '.$this->from.' to '.$this->to.' with cmd "'.$this->cmd.'" failed: '.$ret['stderr'], PEAR_LOG_ERR);
+			}
+			return false;
+		}
 		$end = microtime(true);
 		if($this->logger) {
 			$this->logger->log('Conversion from '.$this->from.' to '.$this->to.' with cmd "'.$this->cmd.'" took '.($end-$start).' sec.', PEAR_LOG_DEBUG);