diff --git a/src/MomentumTransportModels/momentumTransportModels/laminar/generalisedNewtonian/generalisedNewtonianViscosityModels/strainRateViscosityModels/BirdCarreau/BirdCarreau.C b/src/MomentumTransportModels/momentumTransportModels/laminar/generalisedNewtonian/generalisedNewtonianViscosityModels/strainRateViscosityModels/BirdCarreau/BirdCarreau.C
index c22ad783b1..22ab199d2e 100644
--- a/src/MomentumTransportModels/momentumTransportModels/laminar/generalisedNewtonian/generalisedNewtonianViscosityModels/strainRateViscosityModels/BirdCarreau/BirdCarreau.C
+++ b/src/MomentumTransportModels/momentumTransportModels/laminar/generalisedNewtonian/generalisedNewtonianViscosityModels/strainRateViscosityModels/BirdCarreau/BirdCarreau.C
@@ -93,7 +93,7 @@ read
     }
 
     n_.read(coeffs);
-    a_.read(coeffs);
+    a_.readIfPresent(coeffs);
 
     return true;
 }