diff --git a/build.xml b/build.xml
index cdddddcbf..941afaed6 100644
--- a/build.xml
+++ b/build.xml
@@ -86,7 +86,7 @@
 			</else>
 		</if>
 		<echo message="Installing dependencies..." />
-		<exec executable="php" passthru="true" dir="${builddir}/export/${shortversion}">
+		<exec executable="php" passthru="false" dir="${builddir}/export/${shortversion}">
 			<arg line="${srcdir}/composer.phar install ${composer_extra_params}"/>
 			<!-- arg line="${composer_env} php ${srcdir}/composer.phar install ${composer_extra_params}"/ -->
 		</exec>
@@ -218,11 +218,19 @@
 				<copy todir="${builddir}/export/${shortversion}/www/ext/example">
 					<fileset dir="${srcdir}/www/ext/example" defaultexcludes="false" />
 				</copy>
-				<copy todir="${builddir}/export/${shortversion}/www/ext/pdfviewer">
-					<fileset dir="${srcdir}/www/ext/pdfviewer/" expandsymboliclinks="true" defaultexcludes="false">
-						<include name="**/*" />
-					</fileset>
-				</copy>
+				<if>
+					<available file="${srcdir}/www/ext/pdfviewer/conf.php"/>
+					<then>
+						<copy todir="${builddir}/export/${shortversion}/www/ext/pdfviewer">
+							<fileset dir="${srcdir}/www/ext/pdfviewer/" expandsymboliclinks="true" defaultexcludes="false">
+								<include name="**/*" />
+							</fileset>
+						</copy>
+					</then>
+					<else>
+						<echo level="warning" message="I didn't find the extension 'pdfviewer'. You need to install them manually." />
+					</else>
+				</if>
 				<copy tofile="${builddir}/export/${shortversion}/composer.json" file="composer-dist.json">
 					<filterchain>
 						<replaceregexp>