diff --git a/app/Makefile.version b/app/Makefile.version
index 835d0ee0..979a4dde 100644
--- a/app/Makefile.version
+++ b/app/Makefile.version
@@ -3,4 +3,4 @@ APPVERSION_M=2
 # This is the `spec_version` field of `Runtime`
 APPVERSION_N=35
 # This is the patch version of this release
-APPVERSION_P=25
+APPVERSION_P=26
diff --git a/app/src/common/parser_common.h b/app/src/common/parser_common.h
index 95e8f9be..bd437a66 100644
--- a/app/src/common/parser_common.h
+++ b/app/src/common/parser_common.h
@@ -22,6 +22,14 @@ extern "C" {
 #include <stdint.h>
 #include <stddef.h>
 
+#if defined(TARGET_NANOS2) || defined(TARGET_STAX) || defined(TARGET_FLEX)
+#define TX_BUFFER_SIZE 16384
+#elif defined(TARGET_NANOX)
+#define TX_BUFFER_SIZE 16384
+#elif defined(TARGET_NANOS)
+#define TX_BUFFER_SIZE 8192
+#endif
+
 #define CHECK_PARSER_ERR(__CALL) { \
     parser_error_t __err = __CALL;  \
     CHECK_APP_CANARY()  \
diff --git a/app/src/json/json_parser.c b/app/src/json/json_parser.c
index e7adf3f5..cc6741f1 100644
--- a/app/src/json/json_parser.c
+++ b/app/src/json/json_parser.c
@@ -22,6 +22,14 @@
 #define EQUALS(_P, _Q, _LEN) (MEMCMP( (const void*) PIC(_P), (const void*) PIC(_Q), (_LEN))==0)
 
 parser_error_t json_parse(parsed_json_t *parsed_json, const char *buffer, uint16_t bufferLen) {
+    // This check was previously implemented to prevent, here we want to avoid false positives.
+    // It is especially important in fuzzing environments where this check was omitted.
+#if defined(TARGET_NANOS) || defined(TARGET_NANOS2) || defined(TARGET_NANOX) || defined(TARGET_STAX) || defined(TARGET_FLEX)
+    if (bufferLen > TX_BUFFER_SIZE) {
+        return parser_context_unexpected_size;
+    }
+#endif
+
     jsmn_parser parser;
     jsmn_init(&parser);
 
diff --git a/app/src/tx_validate.c b/app/src/tx_validate.c
index b3956706..057530d3 100644
--- a/app/src/tx_validate.c
+++ b/app/src/tx_validate.c
@@ -37,7 +37,7 @@ int8_t is_space(char c) {
     return 0;
 }
 
-int8_t contains_whitespace(parsed_json_t *json) {
+parser_error_t contains_whitespace(parsed_json_t *json) {
     int start = 0;
     const int last_element_index = json->tokens[0].end;
 
@@ -47,21 +47,26 @@ int8_t contains_whitespace(parsed_json_t *json) {
             const int end = json->tokens[i].start;
             for (int j = start; j < end; j++) {
                 if (is_space(json->buffer[j]) == 1) {
-                    return 1;
+                    return parser_json_contains_whitespace;
                 }
             }
             start = json->tokens[i].end + 1;
         } else {
-            return 0;
+            return parser_ok;
         }
     }
+
+    if (start < 0) {
+        return parser_json_unexpected_error;
+    }
+
     while (start < last_element_index && json->buffer[start] != '\0') {
         if (is_space(json->buffer[start])) {
-            return 1;
+            return parser_json_contains_whitespace;
         }
         start++;
     }
-    return 0;
+    return parser_ok;
 }
 
 int8_t is_sorted(uint16_t first_index,
@@ -128,8 +133,9 @@ int8_t dictionaries_sorted(parsed_json_t *json) {
 }
 
 parser_error_t tx_validate(parsed_json_t *json) {
-    if (contains_whitespace(json) == 1) {
-        return parser_json_contains_whitespace;
+    parser_error_t err = contains_whitespace(json);
+    if (err != parser_ok) {
+        return err;
     }
 
     if (dictionaries_sorted(json) != 1) {
@@ -137,7 +143,6 @@ parser_error_t tx_validate(parsed_json_t *json) {
     }
 
     uint16_t token_index;
-    parser_error_t err;
 
     err = object_get_value(json, 0, "chain_id", &token_index);
     if (err != parser_ok)