diff --git a/plugin.cpp b/plugin.cpp
index 49bdaa25..0fb0837a 100644
--- a/plugin.cpp
+++ b/plugin.cpp
@@ -27,7 +27,7 @@ extern "C" {
 #include "read_json.hpp"
 
 struct writer_arg {
-	int *pipe_orig;
+	int write_to;
 	mvt_layer *layer;
 	unsigned z;
 	unsigned x;
@@ -39,7 +39,7 @@ void *run_writer(void *a) {
 
 	// XXX worry about SIGPIPE?
 
-	FILE *fp = fdopen(wa->pipe_orig[1], "w");
+	FILE *fp = fdopen(wa->write_to, "w");
 	if (fp == NULL) {
 		perror("fdopen (pipe writer)");
 		exit(EXIT_FAILURE);
@@ -208,7 +208,7 @@ mvt_layer parse_layer(int fd, unsigned z, unsigned x, unsigned y, mvt_layer cons
 
 static pthread_mutex_t pipe_lock = PTHREAD_MUTEX_INITIALIZER;
 
-mvt_layer filter_layer(const char *filter, mvt_layer &layer, unsigned z, unsigned x, unsigned y) {
+void setup_filter(const char *filter, int *write_to, int *read_from, pid_t *pid, unsigned z, unsigned x, unsigned y) {
 	// This will create two pipes, a new thread, and a new process.
 	//
 	// The new process will read from one pipe and write to the other, and execute the filter.
@@ -234,11 +234,11 @@ mvt_layer filter_layer(const char *filter, mvt_layer &layer, unsigned z, unsigne
 	std::string x_str = std::to_string(x);
 	std::string y_str = std::to_string(y);
 
-	pid_t pid = fork();
-	if (pid < 0) {
+	*pid = fork();
+	if (*pid < 0) {
 		perror("fork");
 		exit(EXIT_FAILURE);
-	} else if (pid == 0) {
+	} else if (*pid == 0) {
 		// child
 
 		if (dup2(pipe_orig[0], 0) < 0) {
@@ -297,37 +297,51 @@ mvt_layer filter_layer(const char *filter, mvt_layer &layer, unsigned z, unsigne
 			exit(EXIT_FAILURE);
 		}
 
-		writer_arg wa;
-		wa.pipe_orig = pipe_orig;
-		wa.layer = &layer;
-		wa.z = z;
-		wa.x = x;
-		wa.y = y;
+		*write_to = pipe_orig[1];
+		*read_from = pipe_filtered[0];
+	}
+}
 
-		pthread_t writer;
-		if (pthread_create(&writer, NULL, run_writer, &wa) != 0) {
-			perror("pthread_create (filter writer)");
-			exit(EXIT_FAILURE);
-		}
+mvt_layer filter_layer(const char *filter, mvt_layer &layer, unsigned z, unsigned x, unsigned y) {
+	int write_to, read_from;
+	pid_t pid;
+	setup_filter(filter, &write_to, &read_from, &pid, z, x, y);
 
-		layer = parse_layer(pipe_filtered[0], z, x, y, layer);
+	writer_arg wa;
+	wa.write_to = write_to;
+	wa.layer = &layer;
+	wa.z = z;
+	wa.x = x;
+	wa.y = y;
 
+	pthread_t writer;
+	if (pthread_create(&writer, NULL, run_writer, &wa) != 0) {
+		perror("pthread_create (filter writer)");
+		exit(EXIT_FAILURE);
+	}
+
+	layer = parse_layer(read_from, z, x, y, layer);
+
+	if (close(read_from) != 0) {
+		perror("close output from filter");
+		exit(EXIT_FAILURE);
+	}
+
+	while (1) {
 		int stat_loc;
 		if (waitpid(pid, &stat_loc, 0) < 0) {
 			perror("waitpid for filter\n");
 			exit(EXIT_FAILURE);
 		}
-
-		if (close(pipe_filtered[0]) != 0) {
-			perror("close output from filter");
-			exit(EXIT_FAILURE);
+		if (WIFEXITED(stat_loc) || WIFSIGNALED(stat_loc)) {
+			break;
 		}
+	}
 
-		void *ret;
-		if (pthread_join(writer, &ret) != 0) {
-			perror("pthread_join filter writer");
-			exit(EXIT_FAILURE);
-		}
+	void *ret;
+	if (pthread_join(writer, &ret) != 0) {
+		perror("pthread_join filter writer");
+		exit(EXIT_FAILURE);
 	}
 
 	return layer;
diff --git a/plugin.hpp b/plugin.hpp
index b8379da0..de6e450b 100644
--- a/plugin.hpp
+++ b/plugin.hpp
@@ -1 +1,2 @@
 mvt_layer filter_layer(const char *filter, mvt_layer &layer, unsigned z, unsigned x, unsigned y);
+void setup_filter(const char *filter, int *write_to, int *read_from, pid_t *pid, unsigned z, unsigned x, unsigned y);