diff --git a/opm/core/fluid/RockCompressibility.cpp b/opm/core/fluid/RockCompressibility.cpp
index bb6863c29..dac8c37ce 100644
--- a/opm/core/fluid/RockCompressibility.cpp
+++ b/opm/core/fluid/RockCompressibility.cpp
@@ -31,8 +31,8 @@ namespace Opm
         : pref_(0.0),
           rock_comp_(0.0)
     {
-        pref_ = param.getDefault("rock_compressibility_pref", 100*unit::barsa);
-        pref_ = param.getDefault("rock_compressibility", 0.0);
+        pref_ = param.getDefault("rock_compressibility_pref", 100.0)*unit::barsa;
+        rock_comp_ = param.getDefault("rock_compressibility", 0.0)/unit::barsa;
     }
 
     RockCompressibility::RockCompressibility(const EclipseGridParser& deck)
diff --git a/opm/core/fluid/RockCompressibility.hpp b/opm/core/fluid/RockCompressibility.hpp
index bcba5aa56..5ae1a9ba4 100644
--- a/opm/core/fluid/RockCompressibility.hpp
+++ b/opm/core/fluid/RockCompressibility.hpp
@@ -35,6 +35,9 @@ namespace Opm
         RockCompressibility(const EclipseGridParser& deck);
 
         /// Construct from parameters.
+        /// Accepts the following parameters (with defaults).
+        ///    rock_compressibility_pref (100.0)   [given in bar]
+        ///    rock_compressibility      (0.0)     [given in bar^{-1}]
         RockCompressibility(const parameter::ParameterGroup& param);
 
         /// Porosity multiplier.