diff --git a/src/json.c b/src/json.c
index 6ae4484..3e36b0f 100644
--- a/src/json.c
+++ b/src/json.c
@@ -355,8 +355,6 @@
 /**
  * @brief Check if the number can be shortened to zero.
  *
- * The input number must be syntactically valid.
- *
  * @param[in] in Start of input string;
  * @param[in] end End of input string;
  * @return 1 if number is zero, otherwise 0.
@@ -364,13 +362,17 @@
 static ly_bool
 lyjson_number_is_zero(const char *in, const char *end)
 {
-    assert(end >= in);
+    assert(in < end);
 
     if ((in[0] == '-') || (in[0] == '+')) {
         in++;
+        assert(in < end);
     }
     if ((in[0] == '0') && (in[1] == '.')) {
         in += 2;
+        if (!(in < end)) {
+            return 1;
+        }
     }
 
     return lyjson_count_in_row(in, end, '0', 0) == end - in;
diff --git a/tests/utests/basic/test_json.c b/tests/utests/basic/test_json.c
index cabafaa..b2cfafd 100644
--- a/tests/utests/basic/test_json.c
+++ b/tests/utests/basic/test_json.c
@@ -505,6 +505,11 @@
     assert_int_equal(LY_EVALID, lyjson_ctx_new(UTEST_LYCTX, in, &jsonctx));
     CHECK_LOG_CTX("Exponent out-of-bounds in a JSON Number value (1e9999999999999999999).", "Line number 1.");
 
+    str = "-2.1e0.";
+    assert_non_null(ly_in_memory(in, str));
+    assert_int_equal(LY_EVALID, lyjson_ctx_new(UTEST_LYCTX, in, &jsonctx));
+    CHECK_LOG_CTX("Unexpected character \".\" after JSON number.", "Line number 1.");
+
     ly_in_free(in, 0);
 }