diff --git a/src/string.cc b/src/string.cc
index ae454264..a9840d45 100644
--- a/src/string.cc
+++ b/src/string.cc
@@ -100,10 +100,19 @@ String indent(StringView str, StringView indent)
 
 int str_to_int(StringView str)
 {
-    int res = 0;
-    if (sscanf(str.zstr(), "%i", &res) != 1)
-        throw runtime_error(str + "is not a number");
-    return res;
+    unsigned int res = 0;
+    bool negative = false;
+    for (auto it = str.begin(), end = str.end(); it != end; ++it)
+    {
+        const char c = *it;
+        if (it == str.begin() and c == '-')
+            negative = true;
+        else if (c >= '0' and c <= '9')
+            res = res * 10 + c - '0';
+        else
+            throw runtime_error(str + "is not a number");
+    }
+    return negative ? -(int)res : (int)res;
 }
 
 String to_string(int val)
diff --git a/src/unit_tests.cc b/src/unit_tests.cc
index 9fb1bae2..5c43c848 100644
--- a/src/unit_tests.cc
+++ b/src/unit_tests.cc
@@ -139,6 +139,12 @@ void test_string()
     kak_assert(not subsequence_match("tchou kanaky", "tchou  kanaky"));
 
     kak_assert(format("Youhou {1} {} {0} \\{}", 10, "hehe", 5) == "Youhou hehe 5 10 {}");
+
+    kak_assert(str_to_int("5") == 5);
+    kak_assert(str_to_int(to_string(INT_MAX)) == INT_MAX);
+    kak_assert(str_to_int(to_string(INT_MIN)) == INT_MIN);
+    kak_assert(str_to_int("00") == 0);
+    kak_assert(str_to_int("-0") == 0);
 }
 
 void test_keys()