diff --git a/src/dwgsim.c b/src/dwgsim.c
index 39a7945..062f69a 100644
--- a/src/dwgsim.c
+++ b/src/dwgsim.c
@@ -533,8 +533,7 @@ void dwgsim_core(dwgsim_opt_t * opt)
               }
           }
       }
-
-      if(0 == opt->muts_only) {
+	  else {
           if(0 == n_ref && opt->C < 0) {
               n_pairs = opt->N - n_sim;
           }
@@ -606,6 +605,7 @@ void dwgsim_core(dwgsim_opt_t * opt)
               continue;
           }
           else if (n_pairs < 0) { // NB: this should not happen
+              fprintf(stderr, "[dwgsim_core] #4 skip sequence '%s' as not enough pairs found\n", name);
               // not enough pairs
               continue;
           }
@@ -618,6 +618,7 @@ void dwgsim_core(dwgsim_opt_t * opt)
       mut_print(name, &seq, mutseq[0], mutseq[1], opt->fp_mut, opt->fp_vcf);
 
       if(0 == opt->muts_only) {
+		  int num_failed = 0;
           for (ii = 0; ii != n_pairs; ++ii, ++ctr) { // the core loop
               if(0 == (ctr % 10000)) {
                   fprintf(stderr, "\r[dwgsim_core] %llu",
@@ -713,12 +714,8 @@ void dwgsim_core(dwgsim_opt_t * opt)
                                * 5' E2 -----> .... E1 -----> 3'
                                * 3'           ....           5'
                                */
-                              if(0 == opt->is_inner) {
-                                  __gen_read(0, pos + d - s[0], ++i); 
-                              }
-                              else {
-                                  __gen_read(0, pos + s[1] + d, ++i); 
-                              }
+							  int r0_pos = (0 == opt->is_inner) ? (pos + d - s[0]) : (pos + s[1] + d - 1);
+							  __gen_read(0, r0_pos, ++i); 
                               __gen_read(1, pos, ++i);
                           }
                           else { // - strand
@@ -726,13 +723,9 @@ void dwgsim_core(dwgsim_opt_t * opt)
                                * 3'           ....            5'
                                * 5' <----- E1 .... <----- E2  3'
                                */
-                              __gen_read(0, pos + s[0], --i);
-                              if(0 == opt->is_inner) {
-                                  __gen_read(1, pos + d, --i);
-                              }
-                              else {
-                                  __gen_read(1, pos + s[0] + d + s[1], --i);
-                              }
+							  int r1_pos = (0 == opt->is_inner) ? (pos + d - 1) : (pos + s[0] + d + s[1] - 1);
+                              __gen_read(0, pos + s[0] - 1, --i);
+							  __gen_read(1, r1_pos, --i);
                           }
                       }
                       else { // opposite strand
@@ -741,25 +734,17 @@ void dwgsim_core(dwgsim_opt_t * opt)
                                * 5' E1 -----> ....           3'
                                * 3'           .... <----- E2 5'
                                */
+							  int r1_pos = (0 == opt->is_inner) ? (pos + d - 1) : (pos + s[0] + d + s[1] - 1);
                               __gen_read(0, pos, ++i);
-                              if(0 == opt->is_inner) {
-                                  __gen_read(1, pos + d, --i);
-                              }
-                              else {
-                                  __gen_read(1, pos + s[0] + d + s[1], --i);
-                              }
+							  __gen_read(1, r1_pos, --i);
                           }
                           else { // - strand
                               /*
                                * 5' E2 -----> ....           3'
                                * 3'           .... <----- E1 5'
                                */
-                              if(0 == opt->is_inner) {
-                                  __gen_read(0, pos + d, --i);
-                              }
-                              else {
-                                  __gen_read(0, pos + s[1] + d + s[0], --i); 
-                              }
+							  int r0_pos = (0 == opt->is_inner) ? (pos + d - 1) : (pos + s[1] + d + s[0] - 1); 
+							  __gen_read(0, r0_pos, --i);
                               __gen_read(1, pos, i++);
                           }
                       }
@@ -786,8 +771,14 @@ void dwgsim_core(dwgsim_opt_t * opt)
                   if (ext_coor[0] < 0 || ext_coor[1] < 0 || opt->max_n < num_n[0] || opt->max_n < num_n[1]) { // fail to generate the read(s)
                       --ii;
                       --ctr;
+					  num_failed++;
+					  if (num_failed > 10000) {
+						  fprintf(stderr, "\r[dwgsim_core] failed to generate a read after %d trials\n", num_failed);
+						  exit(1);
+					  }
                       continue;
                   }
+				  num_failed = 0;
 
                   if(SOLID == opt->data_type) {
                       // Convert to color sequence, use the first base as the adaptor
diff --git a/testdata/ex1.test.bfast.fastq.gz b/testdata/ex1.test.bfast.fastq.gz
index 85bfb18..b343892 100644
Binary files a/testdata/ex1.test.bfast.fastq.gz and b/testdata/ex1.test.bfast.fastq.gz differ
diff --git a/testdata/ex1.test.bwa.read1.fastq.gz b/testdata/ex1.test.bwa.read1.fastq.gz
index 7c76e0c..7e115c9 100644
Binary files a/testdata/ex1.test.bwa.read1.fastq.gz and b/testdata/ex1.test.bwa.read1.fastq.gz differ
diff --git a/testdata/ex1.test.bwa.read2.fastq.gz b/testdata/ex1.test.bwa.read2.fastq.gz
index af52b17..e7003e1 100644
Binary files a/testdata/ex1.test.bwa.read2.fastq.gz and b/testdata/ex1.test.bwa.read2.fastq.gz differ
diff --git a/testdata/test.sh b/testdata/test.sh
index 88b6761..7ab96a2 100644
--- a/testdata/test.sh
+++ b/testdata/test.sh
@@ -15,16 +15,17 @@ popd
 mkdir tmp
 
 # Generate the new test data
-./dwgsim -z 13 -N 10000 samtools/examples/ex1.fa ex1.test
+./dwgsim -z 13 -N 10000 samtools/examples/ex1.fa tmp/ex1.test
 
 # Test the differences
-for GZFILE in $(ls -1 ex1.test*gz)
+for GZFILE in $(ls -1 tmp/ex1.test*gz)
 do 
 	gunzip $GZFILE;
-	FILE=$(echo $GZFILE | sed -e 's_.gz$__g');
-	diff -q ${FILE} ${TESTDATADIR}/${FILE}
+    FILE=$(basename $GZFILE .gz);
+	diff -q tmp/${FILE} ${TESTDATADIR}/${FILE}
 done
 
 # Clean up the testdata
 find ${TESTDATADIR} \! -name "*gz" -type f | grep -v sh$ | xargs rm; 
-rm -r tmp;
+
+rm -r tmp