diff --git a/src/functionObjects/field/streamLine/streamLine.C b/src/functionObjects/field/streamLine/streamLine.C
index 0c66a5fce..2947d0d80 100644
--- a/src/functionObjects/field/streamLine/streamLine.C
+++ b/src/functionObjects/field/streamLine/streamLine.C
@@ -311,7 +311,7 @@ bool Foam::functionObjects::streamLine::read(const dictionary& dict)
     Info<< type() << " " << name() << ":" << nl;
 
     dict.lookup("fields") >> fields_;
-    dict.lookup("U") >> UName_;
+    UName_ = dict.lookupOrDefault("U", word("U"));
 
     if (findIndex(fields_, UName_) == -1)
     {
diff --git a/src/functionObjects/field/streamLine/streamLine.H b/src/functionObjects/field/streamLine/streamLine.H
index 7c0995e69..07a124c48 100644
--- a/src/functionObjects/field/streamLine/streamLine.H
+++ b/src/functionObjects/field/streamLine/streamLine.H
@@ -72,7 +72,7 @@ Usage
         Property     | Description             | Required    | Default value
         type         | Type name: streamLine   | yes         |
         setFormat    | Output data type        | yes         |
-        U            | Tracking velocity field name | yes    |
+        U            | Tracking velocity field name | no     | U
         fields       | Fields to sample        | yes         |
         lifetime     | Maximum number of particle tracking steps | yes |
         trackLength  | Tracking segment length | no          |