diff --git a/R/differential_editing.R b/R/differential_editing.R
index fc42b1a..71e13b1 100644
--- a/R/differential_editing.R
+++ b/R/differential_editing.R
@@ -658,7 +658,7 @@ find_scde_sites <- function(
                                            assay.type = "nAlt",
                                            BPPARAM = BPPARAM)
 
-    grps <- unique(sce[[group]])
+    grps <- unique(as.character(sce[[group]]))
     grp_pairs <- as.data.frame(t(utils::combn(grps, 2)))
     colnames(grp_pairs) <- c("first", "second")
 
diff --git a/R/pileup.R b/R/pileup.R
index 03d4874..3d3fd4b 100644
--- a/R/pileup.R
+++ b/R/pileup.R
@@ -278,7 +278,7 @@ setup_valid_regions <- function(bam, chroms, region = NULL, fasta = NULL) {
             msg <- paste(missing_chroms, collapse = "\n")
             cli::cli_warn(c(
                 "the following chromosomes are not present in the fasta file:",
-                "msg"
+                "{msg}"
             ))
             chroms_to_process <- setdiff(chroms_to_process, missing_chroms)
         }
diff --git a/R/sc-pileup.R b/R/sc-pileup.R
index 47448e1..79b413c 100644
--- a/R/sc-pileup.R
+++ b/R/sc-pileup.R
@@ -163,8 +163,7 @@ pileup_cells <- function(bamfiles,
     umi_tag <- check_tag(umi_tag)
 
     valid_regions <- setup_valid_regions(bamfiles[[1]], chroms)
-    chroms_to_process <- valid_regions$chroms
-
+    chroms_to_process <- intersect(valid_regions$chroms, unique(seqnames(sites)))
     sites <- sites[seqnames(sites) %in% chroms_to_process, ]
 
     if (verbose) cli::cli_alert("Beginning pileup")
@@ -197,13 +196,15 @@ pileup_cells <- function(bamfiles,
         )
     } else {
         # operate in parallel over each chromosome
+        sites_grl <- split(sites, seqnames(sites))
+        sites_grl <- sites_grl[intersect(chroms_to_process, names(sites_grl))]
         sces <- bpmapply(get_sc_pileup,
             chrom = chroms_to_process,
             id = chroms_to_process,
+            site = sites_grl,
             MoreArgs = list(
                 bamfn = bf,
                 index = bfi,
-                sites = sites,
                 barcodes = cell_barcodes,
                 outfile_prefix = output_directory,
                 cb_tag = cb_tag,
@@ -292,6 +293,7 @@ get_sc_pileup <- function(bamfn, index, id, sites, barcodes,
         plp_outfns,
         umi_tag,
         pe,
+        fp[["min_mapq"]],
         max(fp$int_args["min_variant_reads"], fp$int_args["min_depth"])
     )
 
diff --git a/src/init.c b/src/init.c
index c04e950..42ff8a1 100644
--- a/src/init.c
+++ b/src/init.c
@@ -6,12 +6,12 @@
 /* .Call calls */
 extern SEXP get_region(SEXP);
 extern SEXP pileup(SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP);
-extern SEXP scpileup(SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP);
+extern SEXP scpileup(SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP, SEXP);
 
 static const R_CallMethodDef CallEntries[] = {
   {".get_region", (DL_FUNC) &get_region, 1},
   {".pileup",(DL_FUNC)  &pileup, 13},
-  {".scpileup",(DL_FUNC) &scpileup, 13},
+  {".scpileup",(DL_FUNC) &scpileup, 14},
   {NULL, NULL, 0}
 };
 
diff --git a/src/plp.c b/src/plp.c
index 5364f74..f27b11a 100644
--- a/src/plp.c
+++ b/src/plp.c
@@ -375,6 +375,8 @@ static int store_counts(PLP_DATA pd, pcounts* pc, const char* ctig,
                         nv = kh_value((pc + i)->pc->var, k);
                         vf = (double) nv / (pc + i)->pc->total;
                         if (vf < conf->min_af) {
+                            char *key = (char *)kh_key((pc + i)->pc->var, k);
+                            free(key);
                             kh_del(str2intmap, (pc + i)->pc->var, k);
                         }
                     }
@@ -387,6 +389,8 @@ static int store_counts(PLP_DATA pd, pcounts* pc, const char* ctig,
                         nv = kh_value((pc + i)->mc->var, k);
                         vf = (double) nv / (pc + i)->mc->total;
                         if (vf < conf->min_af) {
+                            char *key = (char *)kh_key((pc + i)->mc->var, k);
+                            free(key);
                             kh_del(str2intmap, (pc + i)->mc->var, k);
                         }
                     }
@@ -631,7 +635,7 @@ static int run_pileup(char** cbampaths, char** cindexes,
 
     const bam_pileup1_t** plp;
     mplp_ref_t mp_ref = MPLP_REF_INIT;
-    bam_mplp_t iter;
+    bam_mplp_t iter = NULL;
     bam_hdr_t* h = NULL; /* header of first file in input list */
     char* ref;
 
@@ -664,13 +668,17 @@ static int run_pileup(char** cbampaths, char** cindexes,
         data[i] = calloc(1, sizeof(mplp_aux_t));
         data[i]->fp = sam_open(cbampaths[i], "rb");
         if (!data[i]->fp) {
-            Rf_error("[raer internal] failed to open %s: %s\n",
+            REprintf("[raer internal] failed to open %s: %s\n",
                      cbampaths[i], strerror(errno));
+            ret = -1;
+            goto fail;
         }
         if (conf->fai_fname) {
             if (hts_set_fai_filename(data[i]->fp, conf->fai_fname) != 0) {
-                Rf_error("[raer internal] failed to process %s: %s\n",
+                REprintf("[raer internal] failed to process %s: %s\n",
                          conf->fai_fname, strerror(errno));
+                ret = -1;
+                goto fail;
             }
         }
         data[i]->conf = conf;
@@ -678,7 +686,9 @@ static int run_pileup(char** cbampaths, char** cindexes,
 
         h_tmp = sam_hdr_read(data[i]->fp);
         if (!h_tmp) {
-            Rf_error("[raer internal] fail to read the header of %s\n", cbampaths[i]);
+            REprintf("[raer internal] fail to read the header of %s\n", cbampaths[i]);
+            ret = -1;
+            goto fail;
         }
 
         if (conf->reg) {
@@ -686,11 +696,18 @@ static int run_pileup(char** cbampaths, char** cindexes,
             idx = sam_index_load2(data[i]->fp, cbampaths[i], cindexes[i]) ;
 
             if (idx == NULL) {
-                Rf_error("[raer internal] fail to load bamfile index for %s\n", cbampaths[i]);
+                bam_hdr_destroy(h_tmp);
+                REprintf("[raer internal] fail to load bamfile index for %s\n", cbampaths[i]);
+                ret = -1;
+                goto fail;
             }
 
             if ((data[i]->iter=sam_itr_querys(idx, h_tmp, conf->reg)) == 0) {
-                Rf_error("[raer internal] fail to parse region '%s' with %s\n", conf->reg, cbampaths[i]);
+                bam_hdr_destroy(h_tmp);
+                hts_idx_destroy(idx);
+                REprintf("[raer internal] fail to parse region '%s' with %s\n", conf->reg, cbampaths[i]);
+                ret = -1;
+                goto fail;
             }
 
             if (i == 0) {
@@ -889,13 +906,13 @@ static int run_pileup(char** cbampaths, char** cindexes,
     }
 
     fail:
-        if (ret >= 0) finish_PLP_DATA(pd);
+        finish_PLP_DATA(pd);
 
-        bam_mplp_destroy(iter);
-        bam_hdr_destroy(h);
+        if(iter) bam_mplp_destroy(iter);
+        if(h) bam_hdr_destroy(h);
 
         for (i = 0; i < conf->nbam; ++i) {
-            sam_close(data[i]->fp);
+            if(data[i]->fp) sam_close(data[i]->fp);
             if (data[i]->iter) hts_itr_destroy(data[i]->iter);
             free(data[i]);
             clear_pcounts(&plpc[i]);
@@ -908,25 +925,27 @@ static int run_pileup(char** cbampaths, char** cindexes,
 
         }
 
-        free(data);
-        free(plp);
-        free(n_plp);
+        if(data) free(data);
+        if(plp) free(plp);
+        if(n_plp) free(n_plp);
         free(mp_ref.ref[0]);
         free(mp_ref.ref[1]);
 
         if (pall) {
             R_Free(pall->p_ref_pos);
             R_Free(pall->p_alt_pos);
+            R_Free(pall->m_ref_pos);
             R_Free(pall->m_alt_pos);
-            R_Free(pall->m_alt_pos);
+            R_Free(pall->s);
             R_Free(pall);
         }
 
-        R_Free(plpc);
-        if (pd->fps) R_Free(pd->fps);
-        R_Free(pd->pdat);
-
-        if (site_stats) R_Free(site_stats);
+        if(plpc) R_Free(plpc);
+        if(pd->fps) R_Free(pd->fps);
+        if(pd->pdat) R_Free(pd->pdat);
+        if(pd->sdat) R_Free(pd->sdat);
+        if(pd) R_Free(pd);
+        if(site_stats) R_Free(site_stats);
 
     return ret;
 }
diff --git a/src/sc-plp.c b/src/sc-plp.c
index 68cb990..c65de96 100644
--- a/src/sc-plp.c
+++ b/src/sc-plp.c
@@ -68,7 +68,8 @@ static void clear_umi(umimap_t uhash) {
 }
 
 /*! @function
- @abstract  free keys, values and clear cbumi_map_t hashmap
+ @abstract  free UMI values and clear cbumi_map_t hashmap. Keys are retained to
+ be freed at end of pileup loop.
  */
 static void clear_cb_umiset(cbumi_map_t cbhash) {
   khint_t k;
@@ -100,6 +101,7 @@ static void free_hashmaps(cbumi_map_t cbhash, str2intmap_t cbidx) {
   if (cbhash) {
     for (k = kh_begin(cbhash); k < kh_end(cbhash); ++k) {
       if (!kh_exist(cbhash, k)) continue;
+      free((char*) kh_key(cbhash, k));
       cdat = kh_value(cbhash, k);
       clear_umi(cdat->umi);
       kh_destroy(umimap, cdat->umi);
@@ -248,14 +250,13 @@ static int count_record(const bam_pileup1_t* p, sc_mplp_conf_t* conf, payload_t*
 
   if (pld->strand != strand) return (1);
 
-  cb_cpy = strdup(cb);
-
-  k = kh_get(str2intmap, conf->cbidx, cb_cpy);
+  k = kh_get(str2intmap, conf->cbidx, cb);
   if (k == kh_end(conf->cbidx)) {
-    free(cb_cpy);
     return (0);
   }
 
+  cb_cpy = strdup(cb);
+
   k = kh_put(cbumimap, conf->cbmap, cb_cpy, &cret);
   if (cret < 0) {
     free(cb_cpy);
@@ -729,7 +730,7 @@ static int run_scpileup(sc_mplp_conf_t* conf, char* bamfn, char* index, char* ba
 
 fail:
   if (iter) bam_mplp_destroy(iter);
-  bam_hdr_destroy(h);
+  if(h) bam_hdr_destroy(h);
 
   for (i = 0; i < nbam; ++i) {
     sam_close(data[0]->fp);
@@ -737,9 +738,9 @@ static int run_scpileup(sc_mplp_conf_t* conf, char* bamfn, char* index, char* ba
     if (data[0]->idx) hts_idx_destroy(data[0]->idx);
     free(data[0]);
   }
-  free(data);
-  free(plp);
-  free(n_plp);
+  if(data) free(data);
+  if(plp) free(plp);
+  if(n_plp) free(n_plp);
 
   return ret;
 }
@@ -751,7 +752,7 @@ static int set_sc_mplp_conf(sc_mplp_conf_t* conf, int nbams,
                             int n_outfns, char** outfns, char* qregion, regidx_t* idx,
                             int* i_args, double* d_args, int libtype,
                             int n_bcs, char** bcs, char* cbtag, char* umi,
-                            int pe, int min_counts) {
+                            int pe, int min_mapq, int min_counts) {
   conf->is_ss2 = nbams > 1 ? 1 : 0;
 
   conf->fps = R_Calloc(n_outfns, FILE*);
@@ -795,7 +796,6 @@ static int set_sc_mplp_conf(sc_mplp_conf_t* conf, int nbams,
   conf->read_qual.pct    = d_args[3];
   conf->read_qual.minq   = d_args[4];
 
-  conf->min_mq = (conf->min_mq < 0) ? 0 : conf->min_mq;
   conf->min_bq = (conf->min_bq < 0) ? 0 : conf->min_bq;
   conf->max_depth = (!conf->max_depth ) ? 10000: conf->max_depth ;
 
@@ -832,6 +832,7 @@ static int set_sc_mplp_conf(sc_mplp_conf_t* conf, int nbams,
   }
   conf->cb_tag = cbtag;
   conf->pe = pe;
+  conf->min_mq = (min_mapq < 0) ? 0 : min_mapq;
   conf->min_counts = min_counts < 0 ? 0 : min_counts;
   conf->site_idx = 1;
 
@@ -859,6 +860,7 @@ static int write_all_sites(sc_mplp_conf_t* conf) {
             pld->alt);
 
   }
+  regitr_destroy(itr);
   return (1);
 }
 
@@ -867,7 +869,7 @@ static int write_all_sites(sc_mplp_conf_t* conf) {
  */
 static void check_sc_plp_args(SEXP bampaths, SEXP indexes, SEXP qregion, SEXP lst,
                               SEXP barcodes, SEXP cbtag, SEXP int_args, SEXP dbl_args,
-                              SEXP libtype, SEXP outfns, SEXP umi, SEXP pe,
+                              SEXP libtype, SEXP outfns, SEXP umi, SEXP pe, SEXP min_mapq,
                               SEXP min_counts) {
 
   if (!IS_CHARACTER(bampaths) || (LENGTH(bampaths) < 1)) {
@@ -923,6 +925,10 @@ static void check_sc_plp_args(SEXP bampaths, SEXP indexes, SEXP qregion, SEXP ls
     Rf_error("'pe' must be logical(1)");
   }
 
+  if (!IS_INTEGER(min_mapq) || (LENGTH(min_mapq) != 1)) {
+      Rf_error("'min_mapq' must be integer(1)");
+  }
+
   if (!IS_INTEGER(min_counts) || (LENGTH(min_counts) != 1)) {
     Rf_error("'min_counts' must be integer(1)");
   }
@@ -935,11 +941,11 @@ static void check_sc_plp_args(SEXP bampaths, SEXP indexes, SEXP qregion, SEXP ls
 SEXP scpileup(SEXP bampaths, SEXP indexes, SEXP query_region, SEXP lst,
               SEXP barcodes, SEXP cbtag, SEXP int_args, SEXP dbl_args,
               SEXP libtype,  SEXP outfns, SEXP umi,
-              SEXP pe, SEXP min_counts) {
+              SEXP pe, SEXP min_mapq, SEXP min_counts) {
 
   check_sc_plp_args(bampaths, indexes, query_region, lst,
                     barcodes, cbtag, int_args, dbl_args, libtype,
-                    outfns, umi, pe, min_counts);
+                    outfns, umi, pe, min_mapq, min_counts);
 
   regidx_t* idx = regidx_build(lst, 1);
   if (!idx) Rf_error("Failed to build region index");
@@ -985,7 +991,8 @@ SEXP scpileup(SEXP bampaths, SEXP indexes, SEXP query_region, SEXP lst,
                          cq_region, idx,
                          INTEGER(int_args), REAL(dbl_args),
                          INTEGER(libtype)[0], nbcs, bcs, c_cbtag, c_umi,
-                         LOGICAL(pe)[0], INTEGER(min_counts)[0]);
+                         LOGICAL(pe)[0], INTEGER(min_mapq)[0],
+                         INTEGER(min_counts)[0]);
 
   if (ret >= 0) {
     // write barcodes file, all barcodes will be reported in matrix
diff --git a/tests/testthat/test_pileup_sites.R b/tests/testthat/test_pileup_sites.R
index 266e09a..9dc1008 100644
--- a/tests/testthat/test_pileup_sites.R
+++ b/tests/testthat/test_pileup_sites.R
@@ -104,7 +104,7 @@ test_that("pileup regional query works", {
     expect_equal(end(res), c(203, 204, 205))
 
     # chr1 does not exist
-    expect_error(suppressWarnings(pileup_sites(bamfn, fafn, region = "chr1")))
+    expect_error(pileup_sites(bamfn, fafn, region = "chr1"))
 
     res <- pileup_sites(bamfn, fafn, chrom = "SSR3")
     expect_equal(nrow(res), 529)
@@ -112,7 +112,7 @@ test_that("pileup regional query works", {
 
 test_that("incorrect regional query is caught", {
     # will produce warning that chrHello is not in bamfile and an error
-    expect_error(suppressWarnings(pileup_sites(bamfn, fafn, region = "chrHello")))
+    expect_error(pileup_sites(bamfn, fafn, region = "chrHello"))
 })
 
 test_that("missing files are caught", {