diff --git a/c/data/nlines/1 b/c/data/nlines/1
deleted file mode 100644
index 928a8893c..000000000
--- a/c/data/nlines/1
+++ /dev/null
@@ -1 +0,0 @@
-a=wye,b=eks,i=0,x=0.641593543645736508,y=0.262688053894177098
diff --git a/c/data/nlines/10 b/c/data/nlines/10
new file mode 100644
index 000000000..aa771bb87
--- /dev/null
+++ b/c/data/nlines/10
@@ -0,0 +1,10 @@
+a=wye,b=eks,i=0,x=0.641593543645736508,y=0.262688053894177098
+a=eks,b=zee,i=1,x=0.827614412562742041,y=0.715431942006308552
+a=zee,b=zee,i=2,x=0.923068348748175560,y=0.009737410587136359
+a=zee,b=pan,i=3,x=0.000047786161325772,y=0.803142013402256216
+a=zee,b=hat,i=4,x=0.676537984365847889,y=0.573903236805416328
+a=eks,b=pan,i=5,x=0.097245026890768221,y=0.397166953141413148
+a=zee,b=eks,i=6,x=0.508101613497408899,y=0.663818050950680916
+a=pan,b=wye,i=7,x=0.833840054382495643,y=0.349794006603674046
+a=eks,b=wye,i=8,x=0.350414154748625195,y=0.410698860143636768
+a=wye,b=hat,i=9,x=0.393088969119400222,y=0.646303989759787867
diff --git a/c/tools/catm.c b/c/tools/catm.c
index 49b4b8d7f..8d72a6cc3 100644
--- a/c/tools/catm.c
+++ b/c/tools/catm.c
@@ -29,7 +29,7 @@ static int do_stream(char* file_name) {
 		perror("fstat");
 		exit(1);
 	}
-	char* sof = mmap(NULL, (size_t)stat.st_size, PROT_READ, MAP_FILE|MAP_PRIVATE, fd, (off_t)0);
+	char* sof = mmap(NULL, (size_t)stat.st_size, PROT_READ|PROT_WRITE, MAP_FILE|MAP_PRIVATE, fd, (off_t)0);
 	if (sof == MAP_FAILED) {
 		perror("mmap");
 		exit(1);
@@ -41,9 +41,10 @@ static int do_stream(char* file_name) {
 
 	while (p < eof) {
 		if (*p == '\n') {
-			p++;
+			*p = 0;
 			eol = p;
 			emit(sol, eol, output_stream);
+			p++;
 			sol = p;
 		} else {
 			p++;