diff --git a/external/Makefile b/external/Makefile
index e199108bf..a289032a5 100644
--- a/external/Makefile
+++ b/external/Makefile
@@ -53,6 +53,10 @@ else
 LDLIBS += -lsodium
 endif
 
+ifeq ($(HAVE_ZLIB),1)
+LDLIBS += -lz
+endif
+
 EXTERNAL_LDLIBS := -L${TARGET_DIR} $(patsubst lib%.a,-l%,$(notdir $(EXTERNAL_LIBS)))
 
 submodcheck: $(FORCE)
diff --git a/plugins/askrene/test/Makefile b/plugins/askrene/test/Makefile
index 45aa8feab..88ee0b88a 100644
--- a/plugins/askrene/test/Makefile
+++ b/plugins/askrene/test/Makefile
@@ -10,7 +10,7 @@ $(PLUGIN_RENEPAY_TEST_OBJS): $(PLUGIN_ASKRENE_SRC)
 
 PLUGIN_ASKRENE_TEST_COMMON_OBJS :=
 
-plugins/askrene/test/run-bfs plugins/askrene/test/run-dijkstra plugins/askrene/test/run-flow plugins/askrene/test/run-mcf: \
+plugins/askrene/test/run-bfs plugins/askrene/test/run-dijkstra plugins/askrene/test/run-flow plugins/askrene/test/run-mcf plugins/askrene/test/run-mcf-large: \
 	plugins/askrene/priorityqueue.o \
 	plugins/askrene/graph.o
 
diff --git a/plugins/askrene/test/data/linear_mcf.gz b/plugins/askrene/test/data/linear_mcf.gz
new file mode 100644
index 000000000..b101fd557
Binary files /dev/null and b/plugins/askrene/test/data/linear_mcf.gz differ
diff --git a/plugins/askrene/test/run-mcf-large.c b/plugins/askrene/test/run-mcf-large.c
new file mode 100644
index 000000000..40acc149d
--- /dev/null
+++ b/plugins/askrene/test/run-mcf-large.c
@@ -0,0 +1,136 @@
+#include "config.h"
+#include <assert.h>
+#include <ccan/tal/tal.h>
+#include <common/setup.h>
+#include <inttypes.h>
+#include <plugins/askrene/graph.h>
+#include <stdio.h>
+
+#include "../algorithm.c"
+
+#ifdef HAVE_ZLIB
+#include <zlib.h>
+
+gzFile infile;
+#define BUFFER_SIZE 10000
+char buffer[BUFFER_SIZE];
+
+static int myscanf(const char *fmt, ...)
+{
+	gzgets(infile, buffer, BUFFER_SIZE);
+	va_list args;
+	va_start(args, fmt);
+	int ret = vsscanf(buffer, fmt, args);
+	va_end(args);
+	return ret;
+}
+
+#endif
+
+#define CHECK(arg) if(!(arg)){fprintf(stderr, "failed CHECK at line %d: %s\n", __LINE__, #arg); abort();}
+
+/* Read multiple testcases from a file.
+ * Each test case consist of:
+ * - one line with N and M, the number of nodes and arcs
+ * - for each arc a line with numbers head, tail, cap and cost, defining the
+ * arc's endpoints and values,
+ * - one line with numbers: amount and best_cost, indicating that we wish to
+ *   send amount from node 0 to node 1 with minimum cost, the correct answer
+ *   should contain a flow cost equal to best_cost.
+ *
+ * A feasible solution is guaranteed.
+ * The last test case has 0 nodes and should be ignored. */
+
+static int next_bit(s64 x)
+{
+	int b;
+	for (b = 0; (1LL << b) <= x; b++)
+		;
+	return b;
+}
+
+static bool solve_case(const tal_t *ctx)
+{
+	static int c = 0;
+	c++;
+	tal_t *this_ctx = tal(ctx, tal_t);
+
+	int N_nodes, N_arcs;
+	scanf("%d %d\n", &N_nodes, &N_arcs);
+	printf("Testcase %d\n", c);
+	printf("nodes %d arcs %d\n", N_nodes, N_arcs);
+	if (N_nodes == 0 && N_arcs == 0)
+		goto fail;
+
+	const int MAX_NODES = N_nodes;
+	const int DUAL_BIT = next_bit(N_arcs-1);
+	const int MAX_ARCS = 1LL << (DUAL_BIT+1);
+	printf("max nodes %d max arcs %d bit %d\n", MAX_NODES, MAX_ARCS, DUAL_BIT);
+
+	struct graph *graph = graph_new(ctx, MAX_NODES, MAX_ARCS, DUAL_BIT);
+	assert(graph);
+
+	s64 *capacity = tal_arrz(ctx, s64, MAX_ARCS);
+	s64 *cost = tal_arrz(ctx, s64, MAX_ARCS);
+
+	for (u32 i = 0; i < N_arcs; i++) {
+		u32 from, to;
+		scanf("%" PRIu32 " %" PRIu32 " %" PRIi64 " %" PRIi64, &from,
+		      &to, &capacity[i], &cost[i]);
+
+		struct arc arc = {.idx = i};
+		graph_add_arc(graph, arc, node_obj(from), node_obj(to));
+
+		struct arc dual = arc_dual(graph, arc);
+		cost[dual.idx] = -cost[i];
+	}
+	printf("Reading arcs finished\n");
+	struct node src = {.idx = 0};
+	struct node dst = {.idx = 1};
+
+	s64 amount, best_cost;
+	scanf("%" PRIi64 " %" PRIi64, &amount, &best_cost);
+
+	bool result = simple_mcf(ctx, graph, src, dst, capacity, amount, cost);
+	assert(result);
+
+	assert(node_balance(graph, src, capacity) == -amount);
+	assert(node_balance(graph, dst, capacity) == amount);
+
+	for (u32 i = 2; i < N_nodes; i++)
+		assert(node_balance(graph, node_obj(i), capacity) == 0);
+
+	const s64 total_cost = flow_cost(graph, capacity, cost);
+	assert(total_cost == best_cost);
+
+	tal_free(this_ctx);
+	return true;
+
+fail:
+	tal_free(this_ctx);
+	return false;
+}
+
+int main(int argc, char *argv[])
+{
+#ifdef HAVE_ZLIB
+	common_setup(argv[0]);
+	infile = gzopen("plugins/askrene/test/data/linear_mcf.gz", "r");
+	CHECK(infile);
+	const tal_t *ctx = tal(NULL, tal_t);
+	CHECK(ctx);
+
+	/* One test case after another. The last test case has N number of nodes
+	 * and arcs equal to 0 and must be ignored. */
+	while (solve_case(ctx))
+		;
+
+	ctx = tal_free(ctx);
+	gzclose(infile);
+	common_shutdown();
+	return 0;
+#else
+	return 0;
+#endif
+}
+