diff --git a/c/reg_test/expected/out b/c/reg_test/expected/out
index acf7391bfa..80d7497e23 100644
--- a/c/reg_test/expected/out
+++ b/c/reg_test/expected/out
@@ -322,6 +322,57 @@ a=zee,b=wye,i=8,EKS=0.5985540091064224,y=0.976181385699006
 a=hat,b=wye,i=9,EKS=0.03144187646093577,y=0.7495507603507059
 a=pan,b=wye,i=10,EKS=0.5026260055412137,y=0.9526183602969864
 
+mlr label NEW ./reg_test/input/abixy
+NEW=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533
+NEW=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797
+NEW=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776
+NEW=eks,b=wye,i=4,x=0.38139939387114097,y=0.13418874328430463
+NEW=wye,b=pan,i=5,x=0.5732889198020006,y=0.8636244699032729
+NEW=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697
+NEW=eks,b=zee,i=7,x=0.6117840605678454,y=0.1878849191181694
+NEW=zee,b=wye,i=8,x=0.5985540091064224,y=0.976181385699006
+NEW=hat,b=wye,i=9,x=0.03144187646093577,y=0.7495507603507059
+NEW=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864
+
+mlr label a,NEW,c ./reg_test/input/abixy
+a=pan,NEW=pan,c=1,x=0.3467901443380824,y=0.7268028627434533
+a=eks,NEW=pan,c=2,x=0.7586799647899636,y=0.5221511083334797
+a=wye,NEW=wye,c=3,x=0.20460330576630303,y=0.33831852551664776
+a=eks,NEW=wye,c=4,x=0.38139939387114097,y=0.13418874328430463
+a=wye,NEW=pan,c=5,x=0.5732889198020006,y=0.8636244699032729
+a=zee,NEW=pan,c=6,x=0.5271261600918548,y=0.49322128674835697
+a=eks,NEW=zee,c=7,x=0.6117840605678454,y=0.1878849191181694
+a=zee,NEW=wye,c=8,x=0.5985540091064224,y=0.976181385699006
+a=hat,NEW=wye,c=9,x=0.03144187646093577,y=0.7495507603507059
+a=pan,NEW=wye,c=10,x=0.5026260055412137,y=0.9526183602969864
+
+mlr label 1,2,3,4,5,6,7,8 ./reg_test/input/abixy
+1=pan,2=pan,3=1,4=0.3467901443380824,5=0.7268028627434533
+1=eks,2=pan,3=2,4=0.7586799647899636,5=0.5221511083334797
+1=wye,2=wye,3=3,4=0.20460330576630303,5=0.33831852551664776
+1=eks,2=wye,3=4,4=0.38139939387114097,5=0.13418874328430463
+1=wye,2=pan,3=5,4=0.5732889198020006,5=0.8636244699032729
+1=zee,2=pan,3=6,4=0.5271261600918548,5=0.49322128674835697
+1=eks,2=zee,3=7,4=0.6117840605678454,5=0.1878849191181694
+1=zee,2=wye,3=8,4=0.5985540091064224,5=0.976181385699006
+1=hat,2=wye,3=9,4=0.03144187646093577,5=0.7495507603507059
+1=pan,2=wye,3=10,4=0.5026260055412137,5=0.9526183602969864
+
+mlr label d,x,f ./reg_test/input/abixy
+d=pan,x=pan,f=1,y=0.7268028627434533
+d=eks,x=pan,f=2,y=0.5221511083334797
+d=wye,x=wye,f=3,y=0.33831852551664776
+d=eks,x=wye,f=4,y=0.13418874328430463
+d=wye,x=pan,f=5,y=0.8636244699032729
+d=zee,x=pan,f=6,y=0.49322128674835697
+d=eks,x=zee,f=7,y=0.1878849191181694
+d=zee,x=wye,f=8,y=0.976181385699006
+d=hat,x=wye,f=9,y=0.7495507603507059
+d=pan,x=wye,f=10,y=0.9526183602969864
+
+mlr label d,x,d ./reg_test/input/abixy
+mlr label: labels must be unique; got "d"
+
 mlr --csvlite rename -r ^Date_[0-9].*$,Date ./reg_test/input/date1.csv ./reg_test/input/date2.csv
 Name,Date,Extraneous
 Alice,2015-05-14,foo
diff --git a/c/reg_test/run b/c/reg_test/run
index 510dafd0f1..f52c4a9de8 100755
--- a/c/reg_test/run
+++ b/c/reg_test/run
@@ -198,6 +198,12 @@ run_mlr having-fields --none-matching '"^[a-z][a-z][a-z]$"i' $indir/having-field
 run_mlr rename b,BEE,x,EKS $indir/abixy
 run_mlr rename nonesuch,nonesuch,x,EKS $indir/abixy
 
+run_mlr         label NEW             $indir/abixy
+run_mlr         label a,NEW,c         $indir/abixy
+run_mlr         label 1,2,3,4,5,6,7,8 $indir/abixy
+run_mlr         label d,x,f           $indir/abixy
+mlr_expect_fail label d,x,d           $indir/abixy
+
 run_mlr --csvlite rename -r    '^Date_[0-9].*$,Date'  $indir/date1.csv $indir/date2.csv
 run_mlr --csvlite rename -r    '(.*)e(.*),\1EEE\2'    $indir/date1.csv $indir/date2.csv
 run_mlr --csvlite rename -r    '"(.*)e(.*)"i,\1EEE\2' $indir/date1.csv $indir/date2.csv