diff --git a/src/dbns/timeStepping/backwardDualDdtScheme/backwardDualDdtScheme.C b/src/dbns/timeStepping/backwardDualDdtScheme/backwardDualDdtScheme.C
index 362864292..2647606da 100644
--- a/src/dbns/timeStepping/backwardDualDdtScheme/backwardDualDdtScheme.C
+++ b/src/dbns/timeStepping/backwardDualDdtScheme/backwardDualDdtScheme.C
@@ -861,7 +861,7 @@ backwardDualDdtScheme<Type>::fvcDdtConsistentPhiCorr
     );
 
     // Dummy return
-    return tmp<fluxFieldType>(NULL);
+    return tmp<fluxFieldType>(nullptr);
 }
 
 
diff --git a/src/equationReader/equationOperation/equationOperation.H b/src/equationReader/equationOperation/equationOperation.H
index 50be3b138..4acfd1ef4 100644
--- a/src/equationReader/equationOperation/equationOperation.H
+++ b/src/equationReader/equationOperation/equationOperation.H
@@ -279,7 +279,7 @@ public:
                 const label,
                 const label,
                 const label
-            ) const = NULL,
+            ) const = nullptr,
             void (Foam::equationReader::*opScalarFieldFunction_)
             (
                 const equationReader *,
@@ -289,7 +289,7 @@ public:
                 label&,
                 scalarField&,
                 const scalarField&
-            ) const = NULL,
+            ) const = nullptr,
             scalar (Foam::equationReader::*getSourceScalarFunction)
             (
                 const equationReader *,
@@ -297,7 +297,7 @@ public:
                 const label,
                 const label,
                 const label
-            ) const = NULL,
+            ) const = nullptr,
             void (Foam::equationReader::*opScalarFunction)
             (
                 const equationReader *,
@@ -307,7 +307,7 @@ public:
                 label&,
                 scalar&,
                 scalar
-            ) const = NULL,
+            ) const = nullptr,
             dimensionSet (Foam::equationReader::*getSourceDimsFunction)
             (
                 const equationReader *,
@@ -315,7 +315,7 @@ public:
                 const label,
                 const label,
                 const label
-            ) const = NULL,
+            ) const = nullptr,
             void (Foam::equationReader::*opDimsFunction)
             (
                 const equationReader *,
@@ -325,7 +325,7 @@ public:
                 label&,
                 dimensionSet&,
                 dimensionSet
-            ) const = NULL
+            ) const = nullptr
         );