diff --git a/conf/test.config b/conf/test.config
index b3ad7bd..e79bef4 100644
--- a/conf/test.config
+++ b/conf/test.config
@@ -51,7 +51,7 @@ params {
 process {
     withName: MALT_RUN {
         maxForks = 1
-        ext.args = "-m ${params.malt_mode} -J-Xmx12G"
+        ext.args = { "-m ${params.malt_mode} -J-Xmx12G" }
     }
     withName: MEGAN_RMA2INFO_TSV {
         maxForks = 1
diff --git a/conf/test_nopreprocessing.config b/conf/test_nopreprocessing.config
index c87cf6c..eae6144 100644
--- a/conf/test_nopreprocessing.config
+++ b/conf/test_nopreprocessing.config
@@ -45,6 +45,6 @@ params {
 process {
     withName: MALT_RUN {
         maxForks = 1
-        ext.args = "-m ${params.malt_mode} -J-Xmx8G"
+        ext.args = { "-m ${params.malt_mode} -J-Xmx12G" }
     }
 }
diff --git a/conf/test_nothing.config b/conf/test_nothing.config
index 0a969a6..ca75380 100644
--- a/conf/test_nothing.config
+++ b/conf/test_nothing.config
@@ -44,6 +44,6 @@ params {
 process {
     withName: MALT_RUN {
         maxForks = 1
-        ext.args = "-m ${params.malt_mode} -J-Xmx8G"
+        ext.args = { "-m ${params.malt_mode} -J-Xmx12G" }
     }
 }
diff --git a/conf/test_pep.config b/conf/test_pep.config
index 3cd6dd0..6ce788d 100644
--- a/conf/test_pep.config
+++ b/conf/test_pep.config
@@ -37,7 +37,7 @@ params {
 process {
     withName: MALT_RUN {
         maxForks = 1
-        ext.args = "-m ${params.malt_mode} -J-Xmx8G"
+        ext.args = { "-m ${params.malt_mode} -J-Xmx12G" }
     }
     withName: MEGAN_RMA2INFO {
         maxForks = 1