diff --git a/src/meshTools/regionSplit/minData.H b/src/meshTools/regionSplit/minData.H
index b4af3a9111..a9f6e6dbb6 100644
--- a/src/meshTools/regionSplit/minData.H
+++ b/src/meshTools/regionSplit/minData.H
@@ -177,8 +177,8 @@ public:
 
     // IOstream Operators
 
-        friend Ostream& operator<<(Ostream&, const minData&);
-        friend Istream& operator>>(Istream&, minData&);
+        friend inline Ostream& operator<<(Ostream&, const minData&);
+        friend inline Istream& operator>>(Istream&, minData&);
 };
 
 
diff --git a/src/meshTools/regionSplit/minDataI.H b/src/meshTools/regionSplit/minDataI.H
index 88b2a9a2b8..727da38dc2 100644
--- a/src/meshTools/regionSplit/minDataI.H
+++ b/src/meshTools/regionSplit/minDataI.H
@@ -199,7 +199,7 @@ inline bool Foam::minData::operator!=
 
 // * * * * * * * * * * * * * * * Friend Operators  * * * * * * * * * * * * * //
 
-Foam::Ostream& Foam::operator<<
+inline Foam::Ostream& Foam::operator<<
 (
     Foam::Ostream& os,
     const Foam::minData& wDist
@@ -209,7 +209,7 @@ Foam::Ostream& Foam::operator<<
 }
 
 
-Foam::Istream& Foam::operator>>
+inline Foam::Istream& Foam::operator>>
 (
     Foam::Istream& is,
     Foam::minData& wDist