diff --git a/c/input/lrec_reader_csv.c b/c/input/lrec_reader_csv.c
index 3c922dc18..28de46226 100644
--- a/c/input/lrec_reader_csv.c
+++ b/c/input/lrec_reader_csv.c
@@ -69,7 +69,7 @@ typedef struct _lrec_reader_csv_state_t {
 } lrec_reader_csv_state_t;
 
 static slls_t* lrec_reader_csv_get_fields(lrec_reader_csv_state_t* pstate);
-static lrec_t* paste_header_and_data(lrec_reader_csv_state_t* pstate, slls_t* pdata_fields);
+static lrec_t* paste_header_and_data(lrec_reader_csv_state_t* pstate, slls_t* pdata_fields, context_t* pctx);
 
 // ----------------------------------------------------------------
 static lrec_t* lrec_reader_csv_process(void* pvstate, void* pvhandle, context_t* pctx) {
@@ -107,7 +107,7 @@ static lrec_t* lrec_reader_csv_process(void* pvstate, void* pvhandle, context_t*
 		//lrec_t* prec = paste_header_and_data(pstate, pdata_fields);
 		//slls_free(pdata_fields);
 		//return prec;
-		return paste_header_and_data(pstate, pdata_fields);
+		return paste_header_and_data(pstate, pdata_fields, pctx);
 	}
 }
 
@@ -239,19 +239,22 @@ static slls_t* lrec_reader_csv_get_fields(lrec_reader_csv_state_t* pstate) {
 }
 
 // ----------------------------------------------------------------
-static lrec_t* paste_header_and_data(lrec_reader_csv_state_t* pstate, slls_t* pdata_fields) {
+static lrec_t* paste_header_and_data(lrec_reader_csv_state_t* pstate, slls_t* pdata_fields, context_t* pctx) {
 	if (pstate->pheader_keeper->pkeys->length != pdata_fields->length) {
-		// xxx get the pctx->filename in there as well
-		fprintf(stderr, "%s: Header/data length mismatch: %d != %d at line %lld.\n",
-			MLR_GLOBALS.argv0, pstate->pheader_keeper->pkeys->length, pdata_fields->length, pstate->ilno);
+		fprintf(stderr, "%s: Header/data length mismatch (%d != %d) at file \"%s\" line %lld.\n",
+			MLR_GLOBALS.argv0, pstate->pheader_keeper->pkeys->length, pdata_fields->length,
+			pctx->filename, pstate->ilno);
 		exit(1);
 	}
 	lrec_t* prec = lrec_unbacked_alloc();
 	sllse_t* ph = pstate->pheader_keeper->pkeys->phead;
 	sllse_t* pd = pdata_fields->phead;
 	for ( ; ph != NULL && pd != NULL; ph = ph->pnext, pd = pd->pnext) {
+		// Need to deal with heap-fragmentation among other things ...
+		// https://github.com/johnkerl/miller/issues/66
+		//
+		// lrec_put(prec, ph->value, pd->value, LREC_FREE_ENTRY_VALUE);
 		lrec_put_no_free(prec, ph->value, pd->value);
-		//lrec_put(prec, ph->value, pd->value, LREC_FREE_ENTRY_VALUE);
 	}
 	return prec;
 }
diff --git a/c/lib/string_builder.c b/c/lib/string_builder.c
index 849f12180..26ae285b4 100644
--- a/c/lib/string_builder.c
+++ b/c/lib/string_builder.c
@@ -13,7 +13,7 @@ void sb_init(string_builder_t* psb, int alloc_length) {
 	}
 	psb->used_length = 0;
 	psb->alloc_length = alloc_length;
-	psb->buffer = mlr_malloc_or_die(alloc_length); // xxx malloc ...
+	psb->buffer = mlr_malloc_or_die(alloc_length);
 }
 
 // ----------------------------------------------------------------
diff --git a/c/mapping/mapper_filter.c b/c/mapping/mapper_filter.c
index 70bbed2c1..0fc83e480 100644
--- a/c/mapping/mapper_filter.c
+++ b/c/mapping/mapper_filter.c
@@ -41,7 +41,6 @@ static void mapper_filter_free(void* pvstate) {
 		//hss_free(pstate->pevaluator);
 }
 
-// xxx comment me ...
 static mapper_t* mapper_filter_alloc(mlr_dsl_ast_node_t* past) {
 	mapper_filter_state_t* pstate = mlr_malloc_or_die(sizeof(mapper_filter_state_t));
 
diff --git a/c/mapping/mapper_having_fields.c b/c/mapping/mapper_having_fields.c
index 0058d0abe..410768ef1 100644
--- a/c/mapping/mapper_having_fields.c
+++ b/c/mapping/mapper_having_fields.c
@@ -1,14 +1,14 @@
 #include "lib/mlrutil.h"
 #include "containers/lrec.h"
 #include "containers/sllv.h"
-#include "containers/lhmsi.h"
+#include "containers/hss.h"
 #include "mapping/mappers.h"
 #include "cli/argparse.h"
 
 typedef struct _mapper_having_fields_state_t {
-	slls_t*  pfield_names;
-	lhmsi_t* pfield_name_set; // xxx make this a true set now that i wrote one :/ ;)
-	int      criterion;
+	slls_t* pfield_names;
+	hss_t*  pfield_name_set;
+	int     criterion;
 } mapper_having_fields_state_t;
 
 // ----------------------------------------------------------------
@@ -20,7 +20,7 @@ static sllv_t* mapper_having_fields_at_least_process(lrec_t* pinrec, context_t*
 	mapper_having_fields_state_t* pstate = (mapper_having_fields_state_t*)pvstate;
 	int num_found = 0;
 	for (lrece_t* pe = pinrec->phead; pe != NULL; pe = pe->pnext) {
-		if (lhmsi_has_key(pstate->pfield_name_set, pe->key)) {
+		if (hss_has(pstate->pfield_name_set, pe->key)) {
 			num_found++;
 			if (num_found == pstate->pfield_name_set->num_occupied)
 				return sllv_single(pinrec);
@@ -39,7 +39,7 @@ static sllv_t* mapper_having_fields_which_are_process(lrec_t* pinrec, context_t*
 		return NULL;
 	}
 	for (lrece_t* pe = pinrec->phead; pe != NULL; pe = pe->pnext) {
-		if (!lhmsi_has_key(pstate->pfield_name_set, pe->key)) {
+		if (!hss_has(pstate->pfield_name_set, pe->key)) {
 			lrec_free(pinrec);
 			return NULL;
 		}
@@ -53,7 +53,7 @@ static sllv_t* mapper_having_fields_at_most_process(lrec_t* pinrec, context_t* p
 		return sllv_single(NULL); // xxx cmt all of these, in all mappers
 	mapper_having_fields_state_t* pstate = (mapper_having_fields_state_t*)pvstate;
 	for (lrece_t* pe = pinrec->phead; pe != NULL; pe = pe->pnext) {
-		if (!lhmsi_has_key(pstate->pfield_name_set, pe->key)) {
+		if (!hss_has(pstate->pfield_name_set, pe->key)) {
 			lrec_free(pinrec);
 			return NULL; // xxx cmt all of these, in all mappers
 		}
@@ -66,7 +66,7 @@ static void mapper_having_fields_free(void* pvstate) {
 	mapper_having_fields_state_t* pstate = (mapper_having_fields_state_t*)pvstate;
 	if (pstate->pfield_names != NULL)
 		slls_free(pstate->pfield_names);
-	lhmsi_free(pstate->pfield_name_set);
+	hss_free(pstate->pfield_name_set);
 }
 
 static mapper_t* mapper_having_fields_alloc(slls_t* pfield_names, int criterion) {
@@ -74,9 +74,9 @@ static mapper_t* mapper_having_fields_alloc(slls_t* pfield_names, int criterion)
 
 	mapper_having_fields_state_t* pstate = mlr_malloc_or_die(sizeof(mapper_having_fields_state_t));
 	pstate->pfield_names    = pfield_names;
-	pstate->pfield_name_set = lhmsi_alloc();
+	pstate->pfield_name_set = hss_alloc();
 	for (sllse_t* pe = pfield_names->phead; pe != NULL; pe = pe->pnext)
-		lhmsi_put(pstate->pfield_name_set, pe->value, 0);
+		hss_add(pstate->pfield_name_set, pe->value);
 	pstate->criterion = criterion;
 
 	pmapper->pvstate = (void*)pstate;