diff --git a/geojson.c b/geojson.c
index 19ef9fa5..c7596dee 100644
--- a/geojson.c
+++ b/geojson.c
@@ -971,13 +971,83 @@ void do_read_parallel(char *map, long long len, long long initial_offset, const
 	}
 }
 
-void start_parsing(int fd, long long offset, volatile int *is_parsing, pthread_t *previous_reader) {
-#if 0
-	if (pthread_create(previous_reader, NULL, run_start_parsing, start_parsing_args) == 0) {
+struct start_parsing_arg {
+	int fd;
+	long long offset;
+	long long len;
+	volatile int *is_parsing;
+
+	const char *reading;
+	struct reader *reader;
+	volatile long long *progress_seq;
+	struct pool *exclude;
+	struct pool *include;
+	int exclude_all;
+	char *fname;
+	int maxzoom;
+	int basezoom;
+	int source;
+	int nlayers;
+	double droprate;
+	int *initialized;
+	unsigned *initial_x;
+	unsigned *initial_y;
+};
+
+void *run_start_parsing(void *v) {
+	struct start_parsing_arg *a = v;
+
+	char *map = mmap(NULL, a->len, PROT_READ, MAP_PRIVATE, a->fd, 0);
+	if (map == NULL || map == MAP_FAILED) {
+		perror("map intermediate input");
+		exit(EXIT_FAILURE);
+	}
+
+	do_read_parallel(map, a->len, a->offset, a->reading, a->reader, a->progress_seq, a->exclude, a->include, a->exclude_all, a->fname, a->maxzoom, a->basezoom, a->source, a->nlayers, a->droprate, a->initialized, a->initial_x, a->initial_y);
+
+	if (munmap(map, a->len) != 0) {
+		perror("munmap source file");
+	}
+
+	a->is_parsing = 0;
+	free(a);
+
+	return NULL;
+}
+
+void start_parsing(int fd, long long offset, long long len, volatile int *is_parsing, pthread_t *previous_reader, const char *reading, struct reader *reader, volatile long long *progress_seq, struct pool *exclude, struct pool *include, int exclude_all, char *fname, int maxzoom, int basezoom, int source, int nlayers, double droprate, int *initialized, unsigned *initial_x, unsigned *initial_y) {
+	// This has to kick off an intermediate thread to start the parser threads,
+	// so the main thread can get back to reading the next input stage while
+	// the intermediate thread waits for the completion of the parser threads.
+
+	*is_parsing = 1;
+
+	struct start_parsing_arg *spa = malloc(sizeof(struct start_parsing_arg));
+	spa->fd = fd;
+	spa->offset = offset;
+	spa->len = len;
+	spa->is_parsing = is_parsing;
+
+	spa->reading = reading;
+	spa->reader = reader;
+	spa->progress_seq = progress_seq;
+	spa->exclude = exclude;
+	spa->include = include;
+	spa->exclude_all = exclude_all;
+	spa->fname = fname;
+	spa->maxzoom = maxzoom;
+	spa->basezoom = basezoom;
+	spa->source = source;
+	spa->nlayers = nlayers;
+	spa->droprate = droprate;
+	spa->initialized = initialized;
+	spa->initial_x = initial_x;
+	spa->initial_y = initial_y;
+
+	if (pthread_create(previous_reader, NULL, run_start_parsing, spa) != 0) {
 		perror("pthread_create");
 		exit(EXIT_FAILURE);
 	}
-#endif
 }
 
 int read_json(int argc, char **argv, char *fname, const char *layername, int maxzoom, int minzoom, int basezoom, double basezoom_marker_width, sqlite3 *outdb, struct pool *exclude, struct pool *include, int exclude_all, double droprate, int buffer, const char *tmpdir, double gamma, char *prevent, char *additional, int read_parallel) {
@@ -1149,7 +1219,7 @@ int read_json(int argc, char **argv, char *fname, const char *layername, int max
 					perror(readname);
 					exit(EXIT_FAILURE);
 				}
-				FILE *readfp = fdopen(readfd, "w");
+				FILE *readfp = fopen(readname, "w");
 				if (readfp == NULL) {
 					perror(readname);
 					exit(EXIT_FAILURE);
@@ -1175,7 +1245,7 @@ int read_json(int argc, char **argv, char *fname, const char *layername, int max
 						}
 
 						fclose(readfp);
-						start_parsing(readfd, initial_offset, &is_parsing, &previous_reader);
+						start_parsing(readfd, initial_offset, ahead, &is_parsing, &previous_reader, reading, reader, &progress_seq, exclude, include, exclude_all, fname, maxzoom, basezoom, source, nlayers, droprate, initialized, initial_x, initial_y);
 
 						initial_offset += ahead;
 						ahead = 0;
@@ -1203,10 +1273,13 @@ int read_json(int argc, char **argv, char *fname, const char *layername, int max
 				}
 
 				fclose(readfp);
-				start_parsing(readfd, initial_offset, &is_parsing, &previous_reader);
 
-				if (pthread_join(previous_reader, NULL) != 0) {
-					perror("pthread_join");
+				if (ahead > 0) {
+					start_parsing(readfd, initial_offset, ahead, &is_parsing, &previous_reader, reading, reader, &progress_seq, exclude, include, exclude_all, fname, maxzoom, basezoom, source, nlayers, droprate, initialized, initial_x, initial_y);
+
+					if (pthread_join(previous_reader, NULL) != 0) {
+						perror("pthread_join");
+					}
 				}
 			} else {
 				// Plain serial reading