diff --git a/qsiprep/interfaces/eddy.py b/qsiprep/interfaces/eddy.py
index 36130a36..be2567ad 100644
--- a/qsiprep/interfaces/eddy.py
+++ b/qsiprep/interfaces/eddy.py
@@ -141,6 +141,10 @@ def _run_interface(self, runtime):
         return runtime
 
 
+class ExtendedEddyInputSpec(fsl.epi.EddyInputSpec):
+    num_threads = traits.Int(1, usedefault=True, argstr="--nthr=%d")
+
+
 class ExtendedEddyOutputSpec(fsl.epi.EddyOutputSpec):
     shell_PE_translation_parameters = File(
         exists=True, desc=("the translation along the PE-direction between the different shells")
@@ -169,29 +173,15 @@ class ExtendedEddyOutputSpec(fsl.epi.EddyOutputSpec):
 
 
 class ExtendedEddy(fsl.Eddy):
+    input_spec = ExtendedEddyInputSpec
     output_spec = ExtendedEddyOutputSpec
 
-    _num_threads = 1
-
     def __init__(self, **inputs):
         super(ExtendedEddy, self).__init__(**inputs)
-        self.inputs.on_trait_change(self._num_threads_update, "num_threads")
-        if not isdefined(self.inputs.num_threads):
-            self.inputs.num_threads = self._num_threads
-        else:
-            self._num_threads_update()
         self.inputs.on_trait_change(self._use_cuda, "use_cuda")
         if isdefined(self.inputs.use_cuda):
             self._use_cuda()
 
-    def _num_threads_update(self):
-        self._num_threads = self.inputs.num_threads
-        if not isdefined(self.inputs.num_threads):
-            if "OMP_NUM_THREADS" in self.inputs.environ:
-                del self.inputs.environ["OMP_NUM_THREADS"]
-        else:
-            self.inputs.environ["OMP_NUM_THREADS"] = str(self.inputs.num_threads)
-
     def _use_cuda(self):
         self._cmd = "eddy_cuda10.2" if self.inputs.use_cuda else "eddy_cpu"