diff --git a/src/lexer.c b/src/lexer.c
index 0cc6c6e..c793c4d 100644
--- a/src/lexer.c
+++ b/src/lexer.c
@@ -120,7 +120,11 @@ LexerErr tokenize(const char *input, ASTNodeArray *out) {
     while (input[offset] != '\n' && input[offset] != '\0') {
         int current = input[offset];
 
-        if (isdigit(current) && state == WAIT_FOR_NUMBER) {
+        if (isdigit(current)) {
+            if (state != WAIT_FOR_NUMBER) {
+                ASTNodeArray_free(&arr);
+                return LEXER_WRONG_SYNTAX;
+            }
             ASTNode new_node;
             LexerErr result = tokenize_number(input, &offset, &new_node);
 
@@ -131,7 +135,10 @@ LexerErr tokenize(const char *input, ASTNodeArray *out) {
 
             ASTNodeArray_push(&arr, new_node);
             state = WAIT_FOR_OPERATOR;
-        } else if (isoperator(current) && state == WAIT_FOR_OPERATOR) {
+        } else if (isoperator(current)) {
+            if (state != WAIT_FOR_OPERATOR) {
+                return LEXER_WRONG_SYNTAX;
+            }
             ASTNode new_node = {
                 .type = NODE_BINARY_OP,
                 .data.binary.op = current,
diff --git a/test/test_lexer.c b/test/test_lexer.c
index d10b6d2..2506441 100644
--- a/test/test_lexer.c
+++ b/test/test_lexer.c
@@ -45,6 +45,34 @@ static void test_tokenize_normal_expresion(void **state) {
     assert_int_equal(node.data.integer, 789);
 }
 
+static void test_tokenize_unrecognized_symbol(void **state) {
+    (void) state;
+
+    char expr[256] = " 2 j 3 / 66 } 789";
+    ASTNodeArray tokens = {
+        .len = 0,
+        .cap = 0,
+    };
+
+    assert_int_equal(tokenize(expr, &tokens), LEXER_NOT_RECOGNIZED_SYMBOL);
+    assert_int_equal(tokens.len, 0);
+    assert_int_equal(tokens.cap, 0);
+}
+
+static void test_tokenize_wrong_sintax(void **state) {
+    (void) state;
+
+    char expr[256] = "2 3 / 66 789";
+    ASTNodeArray tokens = {
+        .len = 0,
+        .cap = 0,
+    };
+
+    assert_int_equal(tokenize(expr, &tokens), LEXER_WRONG_SYNTAX);
+    assert_int_equal(tokens.len, 0);
+    assert_int_equal(tokens.cap, 0);
+}
+
 static void test_string_to_number_normal(void **state) {
     (void) state;
 
@@ -76,6 +104,8 @@ int main(void) {
         cmocka_unit_test(test_string_to_number_normal),
         cmocka_unit_test(test_string_to_number_overflow),
         cmocka_unit_test(test_tokenize_normal_expresion),
+        cmocka_unit_test(test_tokenize_unrecognized_symbol),
+        cmocka_unit_test(test_tokenize_wrong_sintax),
     };
 
     return cmocka_run_group_tests(tests, NULL, NULL);