diff --git a/include/adt/common.h b/include/adt/common.h
index 8604edacd..a83604c97 100644
--- a/include/adt/common.h
+++ b/include/adt/common.h
@@ -36,7 +36,7 @@
 /* If non-zero, expand the timer macros defined below, otherwise
  * they compile away. */
 #ifndef TRACK_TIMES
-#define TRACK_TIMES 0
+#define TRACK_TIMES (0 && !BUILD_FOR_FUZZER)
 #endif
 
 #if EXPENSIVE_CHECKS && TRACK_TIMES
diff --git a/include/fsm/walk.h b/include/fsm/walk.h
index e1ab5f29e..cb97e989a 100644
--- a/include/fsm/walk.h
+++ b/include/fsm/walk.h
@@ -90,6 +90,11 @@ fsm_walk_edges(const struct fsm *fsm, void *opaque,
  * functionally equivalent cases makes testing dramatically faster,
  * but exploring every edge could be added later.
  *
+ * If randomized is zero then it will generate the first label in the
+ * label set, otherwise a label from the set will be chosen using rand()
+ * (favoring printable characters). The caller can use srand()
+ * beforehand to set a PRNG seed.
+ *
  * Note: fsm is non-const because it calls fsm_trim on the FSM
  * internally. This records the shortest distance from each state to an
  * end state, which is used to prune branches that would not produce
@@ -114,7 +119,7 @@ fsm_generate_matches_cb(const struct fsm *fsm,
     const char *input, size_t input_length,
     fsm_state_t end_state, void *opaque);
 int
-fsm_generate_matches(struct fsm *fsm, size_t max_length,
+fsm_generate_matches(struct fsm *fsm, size_t max_length, int randomized,
     fsm_generate_matches_cb *cb, void *opaque);
 
 /* Callback provided for the most basic use case for
diff --git a/src/fsm/main.c b/src/fsm/main.c
index da65791dd..f9d1bb3b0 100644
--- a/src/fsm/main.c
+++ b/src/fsm/main.c
@@ -770,7 +770,7 @@ main(int argc, char *argv[])
 	}
 
 	if (generate_bounds > 0) {
-		r = fsm_generate_matches(fsm, generate_bounds, fsm_generate_cb_printf_escaped, &opt);
+		r = fsm_generate_matches(fsm, generate_bounds, 0, fsm_generate_cb_printf_escaped, &opt);
 	}
 
 	fsm_free(fsm);
diff --git a/src/libfsm/determinise.c b/src/libfsm/determinise.c
index 559230175..fc7c68ba4 100644
--- a/src/libfsm/determinise.c
+++ b/src/libfsm/determinise.c
@@ -185,8 +185,6 @@ fsm_determinise_with_config(struct fsm *nfa,
 		}
 
 		ac_env.output_count = 0;
-
-		/* All elements in sclosures[] are interned, so they will be freed later. */
 	} while ((curr = stack_pop(stack)));
 
 	{
diff --git a/src/libfsm/gen.c b/src/libfsm/gen.c
index 26a77be1c..8b8551489 100644
--- a/src/libfsm/gen.c
+++ b/src/libfsm/gen.c
@@ -77,6 +77,7 @@ struct gen_ctx {
 	fsm_generate_matches_cb *cb;
 
 	bool done;
+	bool randomized;
 
 	size_t buf_ceil;
 	size_t buf_used;
@@ -106,7 +107,7 @@ struct gen_ctx {
 static bool
 gen_init_outer(struct fsm *fsm, size_t max_length,
     fsm_generate_matches_cb *cb, void *opaque,
-    bool randomized, unsigned seed);
+    bool randomized);
 
 static bool
 gen_init(struct gen_ctx *ctx, struct fsm *fsm);
@@ -139,7 +140,7 @@ static bool
 grow_stack(struct gen_ctx *ctx);
 
 int
-fsm_generate_matches(struct fsm *fsm, size_t max_length,
+fsm_generate_matches(struct fsm *fsm, size_t max_length, int randomized,
     fsm_generate_matches_cb *cb, void *opaque)
 {
 	if (max_length == 0) {
@@ -147,9 +148,13 @@ fsm_generate_matches(struct fsm *fsm, size_t max_length,
 		return 0;
 	}
 
+	if (!fsm_has(fsm, fsm_isend)) {
+		return 1;	/* no end state -> nothing to do */
+	}
+
 	INIT_TIMERS();
 	TIME(&pre);
-	int res = gen_init_outer(fsm, max_length, cb, opaque, false, 0);
+	int res = gen_init_outer(fsm, max_length, cb, opaque, randomized != 0);
 	TIME(&post);
 
 	DIFF_MSEC("fsm_generate_matches", pre, post, NULL);
@@ -199,7 +204,7 @@ fsm_generate_cb_printf(const struct fsm *fsm,
 static bool
 gen_init_outer(struct fsm *fsm, size_t max_length,
     fsm_generate_matches_cb *cb, void *opaque,
-    bool randomized, unsigned seed)
+    bool randomized)
 {
 	int res = false;
 	if (fsm == NULL || cb == NULL || max_length == 0) {
@@ -208,9 +213,6 @@ gen_init_outer(struct fsm *fsm, size_t max_length,
 
 	assert(fsm_all(fsm, fsm_isdfa)); /* DFA-only */
 
-	assert(!randomized);		 /* not yet supported */
-	(void)seed;
-
 #if LOG_GEN > 1
 	fprintf(stderr, "%s: %u states\n", __func__, fsm_countstates(fsm));
 #endif
@@ -224,6 +226,7 @@ gen_init_outer(struct fsm *fsm, size_t max_length,
 		.max_length = max_length,
 		.cb = cb,
 		.opaque = opaque,
+		.randomized = randomized,
 	};
 
 	if (!gen_init(&ctx, fsm)) {
@@ -524,6 +527,55 @@ first_symbol(const uint64_t *symbols)
 	return 0;
 }
 
+static unsigned char
+random_symbol(const uint64_t *symbols)
+{
+	bool has_zero = false;
+	unsigned i = 0;
+
+	/* printable and non-printable character choices */
+	size_t choice_count = 0;
+	unsigned char choices[256];
+	size_t np_choice_count = 0;
+	unsigned char np_choices[256];
+
+	while (i < 256) {
+		const uint64_t w = symbols[i/64];
+		if ((i & 63) == 0 && w == 0) {
+			i += 64;
+			continue;
+		}
+		if (w & (1ULL << (i & 63))) {
+			if (i == 0) {
+				has_zero = true;
+			} else if (isprint(i)) {
+				choices[choice_count++] = (unsigned char)i;
+			} else {
+				np_choices[np_choice_count++] = (unsigned char)i;
+			}
+		}
+		i++;
+	}
+
+	if (choice_count > 0) {
+		const size_t c = rand() % choice_count;
+		return choices[c];
+	}
+
+	if (np_choice_count > 0) {
+		const size_t c = rand() % np_choice_count;
+		return np_choices[c];
+	}
+
+	/* Prefer anything besides 0x00 if present, since that will truncate the string. */
+	if (has_zero) {
+		return 0;
+	}
+
+	assert(!"empty set");
+	return 0;
+}
+
 #if DUMP_EDGES
 static void
 dump_edges(fsm_state_t state, struct edge_set *edges)
@@ -538,6 +590,7 @@ dump_edges(fsm_state_t state, struct edge_set *edges)
 	size_t i = 0;
 	while (edge_set_group_iter_next(&ei, &eg)) {
 		const unsigned char symbol = first_symbol(eg.symbols);
+		const unsigned char symbol = random_symbol(eg.symbols);
 		fprintf(stderr, "%s: %d -- %zu/%zu -- 0x%02x (%c) -> %d\n",
 		    __func__, state, i, count,
 		    symbol, isprint(symbol) ? symbol : '.', eg.to);
@@ -585,7 +638,9 @@ sfs_step_edges(struct gen_ctx *ctx, struct gen_stack_frame *sf)
 	struct edge_group_iter_info eg;
 
 	if (iter_next_transition(ctx, sf, &eg)) {
-		const unsigned char symbol = first_symbol(eg.symbols);
+		const unsigned char symbol = ctx->randomized
+		    ? random_symbol(eg.symbols)
+		    : first_symbol(eg.symbols);
 		const fsm_state_t state = eg.to;
 
 		LOG(2, "sfs_step_edges: got edge 0x%x ('%c')\n",
diff --git a/src/libfsm/trim.c b/src/libfsm/trim.c
index 4f45607bd..c37965fd8 100644
--- a/src/libfsm/trim.c
+++ b/src/libfsm/trim.c
@@ -462,6 +462,10 @@ integrity_check(const char *descr, const struct fsm *fsm)
 	return;
 #endif
 
+#if !EXPENSIVE_CHECKS
+	return;
+#endif
+
 	if (LOG_TRIM > 1) {
 		fprintf(stderr, "integrity check: %s...\n", descr);
 	}
diff --git a/src/re/main.c b/src/re/main.c
index 62e51f78d..9059af96e 100644
--- a/src/re/main.c
+++ b/src/re/main.c
@@ -1047,7 +1047,7 @@ main(int argc, char *argv[])
 	}
 
 	if (generate_bounds > 0) {
-		if (!fsm_generate_matches(fsm, generate_bounds, fsm_generate_cb_printf_escaped, &opt)) {
+		if (!fsm_generate_matches(fsm, generate_bounds, 0, fsm_generate_cb_printf_escaped, &opt)) {
 			exit(EXIT_FAILURE);
 		}
 
diff --git a/tests/gen/gen1.c b/tests/gen/gen1.c
index 25b30b82b..b25ab2bbc 100644
--- a/tests/gen/gen1.c
+++ b/tests/gen/gen1.c
@@ -34,6 +34,7 @@ int main(void) {
 	assert(fsm != NULL);
 
 	if (!fsm_generate_matches(fsm, MAX_EXP_MATCH + 1 /* for \0 */,
+		0,
 		gtest_matches_cb, &matches)) {
 		fprintf(stderr, "fsm_generate_matches: error\n");
 		exit(EXIT_FAILURE);
diff --git a/tests/gen/gen2.c b/tests/gen/gen2.c
index 02faa5e50..a475e5395 100644
--- a/tests/gen/gen2.c
+++ b/tests/gen/gen2.c
@@ -28,7 +28,7 @@ int main(void) {
 	struct fsm *fsm = gtest_fsm_of_matches(&matches);
 	assert(fsm != NULL);
 
-	if (!fsm_generate_matches(fsm, MAX_EXP_MATCH + 1, gtest_matches_cb, &matches)) {
+	if (!fsm_generate_matches(fsm, MAX_EXP_MATCH + 1, 0, gtest_matches_cb, &matches)) {
 		fprintf(stderr, "fsm_generate_matches: error\n");
 		exit(EXIT_FAILURE);
 	}
diff --git a/tests/gen/gen3.c b/tests/gen/gen3.c
index f24217622..7aa0aebce 100644
--- a/tests/gen/gen3.c
+++ b/tests/gen/gen3.c
@@ -146,7 +146,7 @@ int main(void) {
 	struct fsm *fsm = build();
 	assert(fsm != NULL);
 
-	if (!fsm_generate_matches(fsm, 11, matches_cb, NULL)) {
+	if (!fsm_generate_matches(fsm, 11, 0, matches_cb, NULL)) {
 		fprintf(stderr, "fsm_generate_matches: error\n");
 		exit(EXIT_FAILURE);
 	}