diff --git a/c/mapping/mapper_cat.c b/c/mapping/mapper_cat.c
index 86bd4165e..99fe54443 100644
--- a/c/mapping/mapper_cat.c
+++ b/c/mapping/mapper_cat.c
@@ -97,7 +97,7 @@ static sllv_t* mapper_cat_process(lrec_t* pinrec, context_t* pctx, void* pvstate
 static sllv_t* mapper_catn_process(lrec_t* pinrec, context_t* pctx, void* pvstate) {
 	mapper_cat_state_t* pstate = (mapper_cat_state_t*)pvstate;
 	if (pinrec != NULL) {
-		char* counter_field_value = mlr_alloc_string_from_ull(pstate->counter++);
+		char* counter_field_value = mlr_alloc_string_from_ull(++pstate->counter);
 		lrec_prepend(pinrec, pstate->counter_field_name, counter_field_value, FREE_ENTRY_VALUE);
 		return sllv_single(pinrec);
 	} else {
diff --git a/c/reg_test/expected/out b/c/reg_test/expected/out
index 7bd291bcc..3a7e8751c 100644
--- a/c/reg_test/expected/out
+++ b/c/reg_test/expected/out
@@ -17,28 +17,28 @@ a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864
 mlr cat /dev/null
 
 mlr cat -n ./reg_test/input/abixy
-n=0,a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533
-n=1,a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797
-n=2,a=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776
-n=3,a=eks,b=wye,i=4,x=0.38139939387114097,y=0.13418874328430463
-n=4,a=wye,b=pan,i=5,x=0.5732889198020006,y=0.8636244699032729
-n=5,a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697
-n=6,a=eks,b=zee,i=7,x=0.6117840605678454,y=0.1878849191181694
-n=7,a=zee,b=wye,i=8,x=0.5985540091064224,y=0.976181385699006
-n=8,a=hat,b=wye,i=9,x=0.03144187646093577,y=0.7495507603507059
-n=9,a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864
+n=1,a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533
+n=2,a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797
+n=3,a=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776
+n=4,a=eks,b=wye,i=4,x=0.38139939387114097,y=0.13418874328430463
+n=5,a=wye,b=pan,i=5,x=0.5732889198020006,y=0.8636244699032729
+n=6,a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697
+n=7,a=eks,b=zee,i=7,x=0.6117840605678454,y=0.1878849191181694
+n=8,a=zee,b=wye,i=8,x=0.5985540091064224,y=0.976181385699006
+n=9,a=hat,b=wye,i=9,x=0.03144187646093577,y=0.7495507603507059
+n=10,a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864
 
 mlr cat -N counter ./reg_test/input/abixy
-counter=0,a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533
-counter=1,a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797
-counter=2,a=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776
-counter=3,a=eks,b=wye,i=4,x=0.38139939387114097,y=0.13418874328430463
-counter=4,a=wye,b=pan,i=5,x=0.5732889198020006,y=0.8636244699032729
-counter=5,a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697
-counter=6,a=eks,b=zee,i=7,x=0.6117840605678454,y=0.1878849191181694
-counter=7,a=zee,b=wye,i=8,x=0.5985540091064224,y=0.976181385699006
-counter=8,a=hat,b=wye,i=9,x=0.03144187646093577,y=0.7495507603507059
-counter=9,a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864
+counter=1,a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533
+counter=2,a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797
+counter=3,a=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776
+counter=4,a=eks,b=wye,i=4,x=0.38139939387114097,y=0.13418874328430463
+counter=5,a=wye,b=pan,i=5,x=0.5732889198020006,y=0.8636244699032729
+counter=6,a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697
+counter=7,a=eks,b=zee,i=7,x=0.6117840605678454,y=0.1878849191181694
+counter=8,a=zee,b=wye,i=8,x=0.5985540091064224,y=0.976181385699006
+counter=9,a=hat,b=wye,i=9,x=0.03144187646093577,y=0.7495507603507059
+counter=10,a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864
 
 mlr cut -f a,x ./reg_test/input/abixy
 a=pan,x=0.3467901443380824