diff --git a/src/schema/rules/sidecars/mri.yaml b/src/schema/rules/sidecars/mri.yaml
index ba1d43fda2..3ad7236fa4 100644
--- a/src/schema/rules/sidecars/mri.yaml
+++ b/src/schema/rules/sidecars/mri.yaml
@@ -232,6 +232,7 @@ MRITimingParameters:
         or variable echo time fMRI sequences.
     InversionTime: recommended
     DwellTime: recommended
+    AcquisitionDuration: optional
 
 EchoTimeRequiredASL:
   selectors: