diff --git a/src/common/sstream.c b/src/common/sstream.c
index aabdd6ab..336a65cb 100644
--- a/src/common/sstream.c
+++ b/src/common/sstream.c
@@ -7,6 +7,7 @@
 #include <stdarg.h>
 #include <assert.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <ctype.h>
 
 void c11_sbuf__ctor(c11_sbuf* self) {
@@ -53,21 +54,23 @@ void c11_sbuf__write_f64(c11_sbuf* self, double val, int precision) {
     char b[32];
     int size;
     if(precision < 0) {
-        int prec = 17 - 1;  // std::numeric_limits<double>::max_digits10 == 17
-        size = snprintf(b, sizeof(b), "%.*g", prec, val);
-    } else {
-        int prec = precision;
-        size = snprintf(b, sizeof(b), "%.*f", prec, val);
-    }
-    c11_sbuf__write_cstr(self, b);
-    bool all_is_digit = true;
-    for(int i = 1; i < size; i++) {
-        if(!isdigit(b[i])) {
-            all_is_digit = false;
-            break;
+        size = snprintf(b, sizeof(b), "%.*g", 15, val);
+        if(strtod(b, NULL) != val) {
+            size = snprintf(b, sizeof(b), "%.*g", 17, val);
         }
+        c11_sbuf__write_cstr(self, b);
+        bool all_is_digit = true;
+        for(int i = 1; i < size; i++) {
+            if(!isdigit(b[i])) {
+                all_is_digit = false;
+                break;
+            }
+        }
+        if(all_is_digit) c11_sbuf__write_cstr(self, ".0");
+    } else {
+        size = snprintf(b, sizeof(b), "%.*f", precision, val);
+        c11_sbuf__write_cstr(self, b);
     }
-    if(all_is_digit) c11_sbuf__write_cstr(self, ".0");
 }
 
 void c11_sbuf__write_sv(c11_sbuf* self, c11_sv sv) {
diff --git a/src/compiler/lexer.c b/src/compiler/lexer.c
index bbedf6fc..0d6bedef 100644
--- a/src/compiler/lexer.c
+++ b/src/compiler/lexer.c
@@ -37,16 +37,24 @@ static void Lexer__dtor(Lexer* self) {
     c11_vector__dtor(&self->indents);
 }
 
+static const char* lexer_source_end(Lexer* self) {
+    return self->src->source->data + self->src->source->size;
+}
+
 static char eatchar(Lexer* self) {
+    const char* end = lexer_source_end(self);
+    if(self->curr_char > end) return '\0';
     char c = *self->curr_char;
     assert(c != '\n');  // eatchar() cannot consume a newline
-    self->curr_char++;
+    self->curr_char = (self->curr_char < end) ? self->curr_char + 1 : end + 1;
     return c;
 }
 
 static char eatchar_include_newline(Lexer* self) {
+    const char* end = lexer_source_end(self);
+    if(self->curr_char > end) return '\0';
     char c = *self->curr_char;
-    self->curr_char++;
+    self->curr_char = (self->curr_char < end) ? self->curr_char + 1 : end + 1;
     if(c == '\n') {
         self->current_line++;
         c11_vector__push(const char*, &self->src->line_starts, self->curr_char);
@@ -189,7 +197,8 @@ static Error* LexerError(Lexer* self, const char* fmt, ...) {
     err->src = self->src;
     PK_INCREF(self->src);
     err->lineno = self->current_line;
-    if(*self->curr_char == '\n') { err->lineno--; }
+    const char* end = lexer_source_end(self);
+    if(self->curr_char <= end && *self->curr_char == '\n') { err->lineno--; }
     va_list args;
     va_start(args, fmt);
     vsnprintf(err->msg, sizeof(err->msg), fmt, args);
diff --git a/src/modules/json.c b/src/modules/json.c
index 181d4aff..fca273f6 100644
--- a/src/modules/json.c
+++ b/src/modules/json.c
@@ -102,7 +102,7 @@ static bool json__write_namedict_kv(py_Name k, py_Ref v, void* ctx_) {
 static bool json__write_object(c11_sbuf* buf, py_TValue* obj, int indent, int depth) {
     switch(obj->type) {
         case tp_NoneType: c11_sbuf__write_cstr(buf, "null"); return true;
-        case tp_int: c11_sbuf__write_int(buf, obj->_i64); return true;
+        case tp_int: c11_sbuf__write_i64(buf, obj->_i64); return true;
         case tp_float: {
             if(dmath_isnan(obj->_f64)) {
                 c11_sbuf__write_cstr(buf, "NaN");
diff --git a/src/public/PyList.c b/src/public/PyList.c
index a30c412d..88f2c843 100644
--- a/src/public/PyList.c
+++ b/src/public/PyList.c
@@ -384,7 +384,10 @@ static bool list_insert(int argc, py_Ref argv) {
     return true;
 }
 
-static int lt_with_key(py_TValue* a, py_TValue* b, py_TValue* key) {
+static int lt_with_key(const void* a_, const void* b_, void* extra) {
+    py_TValue* a = (py_TValue*)a_;
+    py_TValue* b = (py_TValue*)b_;
+    py_TValue* key = (py_TValue*)extra;
     if(!key) return py_less(a, b);
     VM* vm = pk_current_vm;
     // project a
@@ -416,7 +419,7 @@ static bool list_sort(int argc, py_Ref argv) {
     bool ok = c11__stable_sort(self->data,
                                self->length,
                                sizeof(py_TValue),
-                               (int (*)(const void*, const void*, void*))lt_with_key,
+                               lt_with_key,
                                key);
     if(!ok) return false;
 
diff --git a/tests/250_rfstring.py b/tests/250_rfstring.py
index 5b687bd6..d2f93ed8 100644
--- a/tests/250_rfstring.py
+++ b/tests/250_rfstring.py
@@ -64,6 +64,7 @@ assert f'{a:010f}' == '010.000000'
 assert f'{a:010.2f}' == '0000010.00'
 assert f'{a:.2f}' == '10.00'
 assert f'{a:.5f}' == '10.00000'
+assert f'{2.5:.0f}' == '2'
 
 b = '123'
 assert f'{b:10}' == '123       '
diff --git a/tests/660_eval.py b/tests/660_eval.py
index 93c3e7a5..f0a88fc0 100644
--- a/tests/660_eval.py
+++ b/tests/660_eval.py
@@ -75,4 +75,11 @@ assert res == [42, 42]
 assert x == 33
 
 # test removing trailing newlines
-assert eval('[1, 2, 3]\n  \n') == [1, 2, 3]
\ No newline at end of file
+assert eval('[1, 2, 3]\n  \n') == [1, 2, 3]
+
+# lexer doesn't read past NUL on error at end of input
+try:
+    eval('"\\x4')
+    exit(1)
+except SyntaxError:
+    pass
\ No newline at end of file
diff --git a/tests/721_json.py b/tests/721_json.py
index 29d168bc..8509d02b 100644
--- a/tests/721_json.py
+++ b/tests/721_json.py
@@ -48,6 +48,9 @@ _j = json.dumps(c)
 _c = json.loads(_j)
 assert c == _c
 
+assert json.dumps(9223372036854775807) == '9223372036854775807'
+assert json.loads(json.dumps(0.1 + 0.2)) == 0.1 + 0.2
+
 d = True
 _j = json.dumps(d)
 _d = json.loads(_j)