diff --git a/lofar-cwl/steps/ms_concat.cwl b/lofar-cwl/steps/ms_concat.cwl
index 6fd74a46486a1de66641f0519ff6ff86c42d959e..fc61241c1e26816e856bd3aa63a0473bff46cdf2 100644
--- a/lofar-cwl/steps/ms_concat.cwl
+++ b/lofar-cwl/steps/ms_concat.cwl
@@ -54,10 +54,11 @@ outputs:
     outputBinding:
       glob: ms_concat.log
 label: ms_concat
-requirements:
-  - class: ShellCommandRequirement
+hints:
   - class: DockerRequirement
     dockerPull: 'lofareosc/prefactor:HBAcalibrator'
+requirements:
+  - class: ShellCommandRequirement
   - class: InitialWorkDirRequirement
     listing:
       - entry: $(inputs.msin)
diff --git a/lofar-cwl/steps/wsclean.cwl b/lofar-cwl/steps/wsclean.cwl
index 08d1e3d6596529d97a9ff5f718a983676afd748c..24af8bd95512ffd5e615a6381c187f61216b3c1a 100644
--- a/lofar-cwl/steps/wsclean.cwl
+++ b/lofar-cwl/steps/wsclean.cwl
@@ -41,7 +41,8 @@ outputs:
     outputBinding:
       glob: $(inputs.image_name)-image.fits
 label: WSClean
-requirements:
+hints:
   - class: DockerRequirement
     dockerPull: 'lofareosc/prefactor:HBAcalibrator'
+requirements:
   - class: InlineJavascriptRequirement
diff --git a/steps/find_skymodel_cal.cwl b/steps/find_skymodel_cal.cwl
index 4d0956951eda01b2d626f12344c73209f97de776..98c665d5adc0ccb56351ecb9d0dc957478b4836c 100644
--- a/steps/find_skymodel_cal.cwl
+++ b/steps/find_skymodel_cal.cwl
@@ -68,7 +68,7 @@ requirements:
             
             skymodels = $(inputs.skymodels)
             max_separation_arcmin = $(inputs.max_separation_arcmin)
-            max_separation_arcmin = 1.0 if max_separation_arcmin else max_separation_arcmin
+            max_separation_arcmin = 1.0 if max_separation_arcmin is None else max_separation_arcmin
             extension = "$(inputs.skymodels_extension)"
             if skymodels is None:
                 skymodels = "/data/skymodels"