diff --git a/mongoose.c b/mongoose.c
index 16ef5a23..4db876fd 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -14707,10 +14707,10 @@ typedef struct _BI_CTX BI_CTX;
  */
 
 NS_INTERNAL BI_CTX *bi_initialize(void);
-//NS_INTERNAL void bi_terminate(BI_CTX *ctx);
+NS_INTERNAL void bi_terminate(BI_CTX *ctx);
 NS_INTERNAL void bi_permanent(bigint *bi);
 NS_INTERNAL void bi_depermanent(bigint *bi);
-//NS_INTERNAL void bi_clear_cache(BI_CTX *ctx);
+NS_INTERNAL void bi_clear_cache(BI_CTX *ctx);
 NS_INTERNAL void bi_free(BI_CTX *ctx, bigint *bi);
 NS_INTERNAL bigint *bi_copy(bigint *bi);
 NS_INTERNAL bigint *bi_clone(BI_CTX *ctx, const bigint *bi);
@@ -14732,7 +14732,7 @@ NS_INTERNAL bigint *bi_mod_power2(BI_CTX *ctx, bigint *bi,
 #endif
 NS_INTERNAL int bi_compare(bigint *bia, bigint *bib);
 NS_INTERNAL void bi_set_mod(BI_CTX *ctx, bigint *bim, int mod_offset);
-//NS_INTERNAL void bi_free_mod(BI_CTX *ctx, int mod_offset);
+NS_INTERNAL void bi_free_mod(BI_CTX *ctx, int mod_offset);
 
 #ifdef CONFIG_SSL_FULL_MODE
 NS_INTERNAL void bi_print(const char *label, bigint *bi);
@@ -14869,7 +14869,6 @@ NS_INTERNAL BI_CTX *bi_initialize(void) {
   return ctx;
 }
 
-#if 0
 /**
  * @brief Close the bigint context and free any resources.
  *
@@ -14909,7 +14908,6 @@ NS_INTERNAL void bi_clear_cache(BI_CTX *ctx) {
   ctx->free_count = 0;
   ctx->free_list = NULL;
 }
-#endif
 
 /**
  * @brief Increment the number of references to this object.
@@ -15479,7 +15477,6 @@ NS_INTERNAL void bi_set_mod(BI_CTX *ctx, bigint *bim, int mod_offset) {
 #endif
 }
 
-#if 0
 /**
  * @brief Used when cleaning various bigints at the end of a session.
  * @param ctx [in]  The bigint session context.
@@ -15501,7 +15498,6 @@ void bi_free_mod(BI_CTX *ctx, int mod_offset) {
   bi_depermanent(ctx->bi_normalised_mod[mod_offset]);
   bi_free(ctx, ctx->bi_normalised_mod[mod_offset]);
 }
-#endif
 
 /**
  * Perform a standard multiplication between two bigints.
@@ -16111,6 +16107,21 @@ NS_INTERNAL bigint *bi_crt(BI_CTX *ctx, bigint *bi, bigint *dP, bigint *dQ,
 }
 #endif
 
+
+// Proper lib usage:
+// - BI_CTX *c = bi_initialize()
+// - allocate bigints (e.g.: calling bi_import(), int_to_bi(), ...)
+// - function calls, allocate bigints, etc.
+// - bigint *n = bi_import(c, indata, insize)
+//   - bi_set_mod(c, n, x)
+//   - mod function calls
+//   - bigint *nn = bi_mod_pwr(c, m, e) <-- frees m, e
+//   - bi_free_mod(c, x)                <-- frees n
+// - bi_export(c, nn, outdata, outsize) <-- frees nn
+// - function calls
+// - free bigints calling bi_free()
+// - bi_terminate(c)                    <-- frees c
+
 int mg_rsa_mod_pow(const uint8_t *mod, size_t modsz, const uint8_t *exp, size_t expsz, const uint8_t *msg, size_t msgsz, uint8_t *out, size_t outsz) {
 	BI_CTX *bi_ctx = bi_initialize();
 	bigint *n = bi_import(bi_ctx, mod, (int) modsz);
@@ -16118,11 +16129,9 @@ int mg_rsa_mod_pow(const uint8_t *mod, size_t modsz, const uint8_t *exp, size_t
 	bigint *h = bi_import(bi_ctx, msg, (int) msgsz);
 	bi_set_mod(bi_ctx, n, 0);
 	bigint *m1 = bi_mod_power(bi_ctx, h, e);
+	bi_free_mod(bi_ctx, 0);
 	bi_export(bi_ctx, m1, out, (int) outsz);
-	bi_free(bi_ctx, n);
-	bi_free(bi_ctx, e);
-	bi_free(bi_ctx, h);
-	bi_free(bi_ctx, m1);
+	bi_terminate(bi_ctx);
 	return 0;
 }
 
diff --git a/src/tls_rsa.c b/src/tls_rsa.c
index b066722e..75300d12 100644
--- a/src/tls_rsa.c
+++ b/src/tls_rsa.c
@@ -159,10 +159,10 @@ typedef struct _BI_CTX BI_CTX;
  */
 
 NS_INTERNAL BI_CTX *bi_initialize(void);
-//NS_INTERNAL void bi_terminate(BI_CTX *ctx);
+NS_INTERNAL void bi_terminate(BI_CTX *ctx);
 NS_INTERNAL void bi_permanent(bigint *bi);
 NS_INTERNAL void bi_depermanent(bigint *bi);
-//NS_INTERNAL void bi_clear_cache(BI_CTX *ctx);
+NS_INTERNAL void bi_clear_cache(BI_CTX *ctx);
 NS_INTERNAL void bi_free(BI_CTX *ctx, bigint *bi);
 NS_INTERNAL bigint *bi_copy(bigint *bi);
 NS_INTERNAL bigint *bi_clone(BI_CTX *ctx, const bigint *bi);
@@ -184,7 +184,7 @@ NS_INTERNAL bigint *bi_mod_power2(BI_CTX *ctx, bigint *bi,
 #endif
 NS_INTERNAL int bi_compare(bigint *bia, bigint *bib);
 NS_INTERNAL void bi_set_mod(BI_CTX *ctx, bigint *bim, int mod_offset);
-//NS_INTERNAL void bi_free_mod(BI_CTX *ctx, int mod_offset);
+NS_INTERNAL void bi_free_mod(BI_CTX *ctx, int mod_offset);
 
 #ifdef CONFIG_SSL_FULL_MODE
 NS_INTERNAL void bi_print(const char *label, bigint *bi);
@@ -321,7 +321,6 @@ NS_INTERNAL BI_CTX *bi_initialize(void) {
   return ctx;
 }
 
-#if 0
 /**
  * @brief Close the bigint context and free any resources.
  *
@@ -361,7 +360,6 @@ NS_INTERNAL void bi_clear_cache(BI_CTX *ctx) {
   ctx->free_count = 0;
   ctx->free_list = NULL;
 }
-#endif
 
 /**
  * @brief Increment the number of references to this object.
@@ -931,7 +929,6 @@ NS_INTERNAL void bi_set_mod(BI_CTX *ctx, bigint *bim, int mod_offset) {
 #endif
 }
 
-#if 0
 /**
  * @brief Used when cleaning various bigints at the end of a session.
  * @param ctx [in]  The bigint session context.
@@ -953,7 +950,6 @@ void bi_free_mod(BI_CTX *ctx, int mod_offset) {
   bi_depermanent(ctx->bi_normalised_mod[mod_offset]);
   bi_free(ctx, ctx->bi_normalised_mod[mod_offset]);
 }
-#endif
 
 /**
  * Perform a standard multiplication between two bigints.
@@ -1563,6 +1559,21 @@ NS_INTERNAL bigint *bi_crt(BI_CTX *ctx, bigint *bi, bigint *dP, bigint *dQ,
 }
 #endif
 
+
+// Proper lib usage:
+// - BI_CTX *c = bi_initialize()
+// - allocate bigints (e.g.: calling bi_import(), int_to_bi(), ...)
+// - function calls, allocate bigints, etc.
+// - bigint *n = bi_import(c, indata, insize)
+//   - bi_set_mod(c, n, x)
+//   - mod function calls
+//   - bigint *nn = bi_mod_pwr(c, m, e) <-- frees m, e
+//   - bi_free_mod(c, x)                <-- frees n
+// - bi_export(c, nn, outdata, outsize) <-- frees nn
+// - function calls
+// - free bigints calling bi_free()
+// - bi_terminate(c)                    <-- frees c
+
 int mg_rsa_mod_pow(const uint8_t *mod, size_t modsz, const uint8_t *exp, size_t expsz, const uint8_t *msg, size_t msgsz, uint8_t *out, size_t outsz) {
 	BI_CTX *bi_ctx = bi_initialize();
 	bigint *n = bi_import(bi_ctx, mod, (int) modsz);
@@ -1570,11 +1581,9 @@ int mg_rsa_mod_pow(const uint8_t *mod, size_t modsz, const uint8_t *exp, size_t
 	bigint *h = bi_import(bi_ctx, msg, (int) msgsz);
 	bi_set_mod(bi_ctx, n, 0);
 	bigint *m1 = bi_mod_power(bi_ctx, h, e);
+	bi_free_mod(bi_ctx, 0);
 	bi_export(bi_ctx, m1, out, (int) outsz);
-	bi_free(bi_ctx, n);
-	bi_free(bi_ctx, e);
-	bi_free(bi_ctx, h);
-	bi_free(bi_ctx, m1);
+	bi_terminate(bi_ctx);
 	return 0;
 }
 
diff --git a/test/unit_test.c b/test/unit_test.c
index e11fa4af..e656beac 100644
--- a/test/unit_test.c
+++ b/test/unit_test.c
@@ -440,9 +440,9 @@ static void mqtt_cb(struct mg_connection *c, int ev, void *ev_data) {
     opts.name = mg_url_host(MQTTS_URL);
 
     mg_tls_init(c, &opts);
-  } else 
+  } else
 #endif
-  if (ev == MG_EV_MQTT_OPEN) {
+      if (ev == MG_EV_MQTT_OPEN) {
     buf[0] = *(int *) ev_data == 0 ? 'X' : 'Y';
   } else if (ev == MG_EV_CLOSE) {
     buf[0] = 0;
@@ -570,7 +570,7 @@ static void test_mqtt_basic(void) {
   struct mg_mqtt_opts opts;
 #if MG_TLS
   const char *url = MQTTS_URL;
-#else 
+#else
   const char *url = "mqtt://broker.hivemq.com:1883";
 #endif
   int i, retries;
@@ -619,14 +619,14 @@ static void test_mqtt_basic(void) {
 
 #if MG_TLS
   // send more than 1 record, content is not relevant
-  opts.message = mg_str_n((char *)(size_t) test_mqtt_basic, 21098);
+  opts.message = mg_str_n((char *) (size_t) test_mqtt_basic, 21098);
   opts.qos = 1, opts.retain = false, opts.retransmit_id = 0;
   mg_mqtt_pub(c, &opts);
   tbuf[0] = 0;
   for (i = 0; i < 1000 && test_data.flags == 0; i++) mg_mgr_poll(&mgr, 10);
   ASSERT(test_data.flags == flags_published);
   for (i = 0; i < 1000 && tbuf[0] == 0; i++) mg_mgr_poll(&mgr, 10);
-  ASSERT(tbuf[0] != 0); // just check we were able to send and receive
+  ASSERT(tbuf[0] != 0);  // just check we were able to send and receive
   memset(mbuf + 1, 0, sizeof(mbuf) - 1);
   test_data.flags = 0;
   opts.retransmit_id = 0;
@@ -3846,12 +3846,69 @@ static void test_x25519(void) {
 #endif
 }
 
+static void test_rsa(void) {
+#if MG_TLS == MG_TLS_BUILTIN
+  const unsigned char mod[] = {
+      0x00, 0xba, 0xee, 0x3b, 0x0b, 0x89, 0x58, 0xa6, 0x19, 0x0d, 0x4c, 0x89,
+      0x1a, 0x85, 0x9a, 0xf4, 0x55, 0xc2, 0xdd, 0x0d, 0xd4, 0x4a, 0xf5, 0xed,
+      0xda, 0x28, 0x55, 0x2f, 0x64, 0x46, 0x21, 0x9f, 0x46, 0x5c, 0xfa, 0x37,
+      0x88, 0x11, 0xdf, 0xcb, 0x51, 0x73, 0x42, 0x3d, 0x5e, 0x50, 0xde, 0x11,
+      0x30, 0x61, 0x04, 0x59, 0xd0, 0xf4, 0x57, 0xed, 0x13, 0x90, 0x32, 0xc5,
+      0x3f, 0xe6, 0x66, 0xfc, 0x2a, 0x12, 0xa3, 0x1f, 0xd1, 0x77, 0x21, 0x65,
+      0xdf, 0x9a, 0xcf, 0x04, 0x05, 0xc3, 0x1c, 0xf8, 0x79, 0xb5, 0xf5, 0x97,
+      0x68, 0x98, 0x2e, 0x96, 0x85, 0x3f, 0xee, 0x71, 0x91, 0xc1, 0x54, 0x71,
+      0x9a, 0x80, 0x1f, 0xbe, 0x21, 0xd9, 0xc1, 0x80, 0x9b, 0xd0, 0x5d, 0xb3,
+      0x76, 0x3e, 0xcc, 0x14, 0x3d, 0xec, 0xb7, 0x18, 0x74, 0xfb, 0xc4, 0x0e,
+      0x56, 0x8d, 0x3d, 0x78, 0xe6, 0xca, 0xcd, 0x9d, 0xc6, 0x20, 0x5a, 0xeb,
+      0x9b, 0xc8, 0x19, 0x5e, 0xeb, 0x80, 0xd2, 0xb2, 0xfe, 0x88, 0x15, 0x5c,
+      0x7c, 0x6b, 0x26, 0xe0, 0x43, 0xda, 0xa4, 0x07, 0x85, 0x73, 0xc4, 0x80,
+      0x28, 0xcb, 0xda, 0x18, 0x56, 0x37, 0x91, 0xd6, 0x41, 0xa1, 0x0b, 0xa2,
+      0x77, 0xd0, 0x62, 0x31, 0xc7, 0xc2, 0x67, 0x6d, 0x75, 0x08, 0x80, 0xe7,
+      0xb6, 0xbe, 0xc2, 0x25, 0xc9, 0xe0, 0x2c, 0x02, 0xbf, 0x39, 0x61, 0x7e,
+      0x32, 0xa4, 0xc9, 0xe7, 0x91, 0xe3, 0xa0, 0xcd, 0x94, 0x24, 0xbf, 0x8c,
+      0xeb, 0x47, 0x76, 0x53, 0x85, 0xb3, 0xb7, 0x31, 0x80, 0x3c, 0x77, 0x10,
+      0x69, 0xc3, 0x04, 0xd1, 0x60, 0x4c, 0x74, 0xda, 0x15, 0x18, 0x0b, 0x20,
+      0x6f, 0xb3, 0x03, 0x58, 0x4a, 0xfc, 0xd1, 0xd2, 0xcf, 0x37, 0x15, 0x0a,
+      0x63, 0xc8, 0xe9, 0xd5, 0x7d, 0xd5, 0xf2, 0x90, 0x78, 0x53, 0x49, 0xa9,
+      0xc5, 0x25, 0x65, 0x5c, 0x01};
+  const unsigned char exp[] = {1, 0, 1};  // 65537
+  const unsigned char sig[] = {
+      0x1e, 0xb1, 0x6a, 0xcb, 0x39, 0x63, 0x12, 0xed, 0x85, 0x62, 0x4b, 0x85,
+      0x47, 0x25, 0x67, 0xbd, 0xbd, 0x0e, 0xaa, 0x73, 0x34, 0x5f, 0x07, 0x2b,
+      0xbb, 0x4f, 0xf5, 0x21, 0x88, 0xb1, 0x04, 0x2c, 0xbb, 0x52, 0x72, 0x64,
+      0x89, 0x45, 0x50, 0x41, 0x73, 0xca, 0xda, 0x97, 0xae, 0x81, 0x89, 0x4f,
+      0x83, 0x8d, 0x48, 0x65, 0x63, 0xe7, 0x82, 0x03, 0xd2, 0x40, 0x07, 0x1c,
+      0x86, 0x58, 0xd5, 0xac, 0x89, 0xb1, 0xca, 0x5c, 0xde, 0x21, 0x06, 0x88,
+      0x88, 0x0c, 0xe1, 0x20, 0xc0, 0xdf, 0xf1, 0x92, 0x9b, 0xb8, 0xa5, 0xeb,
+      0x6d, 0x89, 0xcc, 0x5c, 0x5c, 0x24, 0x3e, 0x9b, 0x3c, 0x35, 0x32, 0xa5,
+      0x04, 0x9e, 0x8c, 0x49, 0x01, 0xee, 0xbf, 0x1f, 0x2c, 0xb0, 0x52, 0xa8,
+      0xab, 0x79, 0x11, 0xcf, 0xb5, 0x5a, 0x16, 0xa1, 0xee, 0x21, 0x6a, 0x5a,
+      0x2b, 0x14, 0xae, 0x32, 0x3c, 0xa2, 0x6c, 0xa2, 0x40, 0x0c, 0xcb, 0x9e,
+      0x8f, 0x69, 0xab, 0xd7, 0xf3, 0xd8, 0xd1, 0xfb, 0x2d, 0xfa, 0xa9, 0x13,
+      0x09, 0xbf, 0xa7, 0xca, 0xc8, 0x90, 0x74, 0x23, 0x7b, 0x3e, 0xdd, 0x81,
+      0x32, 0xa7, 0x88, 0x42, 0x56, 0x8a, 0xcb, 0xe8, 0x8f, 0xef, 0x06, 0x9f,
+      0x39, 0x7e, 0x8e, 0x24, 0x07, 0xb3, 0xae, 0x7e, 0x13, 0x6b, 0xf2, 0xf8,
+      0x35, 0xe4, 0x16, 0x3e, 0xae, 0xf2, 0x55, 0x79, 0x10, 0x39, 0xfa, 0x70,
+      0x3a, 0x1b, 0x02, 0xb3, 0x2b, 0x1d, 0x44, 0xac, 0x30, 0x81, 0xd3, 0x11,
+      0xdd, 0x34, 0x1e, 0xcd, 0x26, 0xf5, 0x89, 0xc6, 0x55, 0x23, 0x17, 0x09,
+      0xd2, 0xc1, 0xdc, 0x49, 0xf9, 0x99, 0x36, 0x2b, 0xf5, 0xae, 0x42, 0x5c,
+      0xb7, 0x80, 0xda, 0x32, 0x69, 0x28, 0xa3, 0xee, 0xb9, 0xd4, 0x90, 0xa6,
+      0xab, 0x34, 0x17, 0x5e, 0xa0, 0xd6, 0xc1, 0x54, 0xc6, 0x9c, 0x58, 0x3a,
+      0xaf, 0xbf, 0xdc, 0x64};
+  unsigned char v[256];  // 2048 bits
+  mg_rsa_mod_pow(mod, sizeof(mod), exp, sizeof(exp), sig, sizeof(sig), v,
+                 sizeof(v));
+  ASSERT(v[sizeof(v) - 1] == 0xbc);
+#endif
+}
+
 static void test_crypto(void) {
   test_md5();
   test_sha1();
   test_sha256();
   test_sha384();
   test_x25519();
+  test_rsa();
 }
 
 int main(void) {