diff --git a/libc/stdio/fmt.c b/libc/stdio/fmt.c
index a866b196f..6f42e9b39 100644
--- a/libc/stdio/fmt.c
+++ b/libc/stdio/fmt.c
@@ -1073,6 +1073,9 @@ int __fmt(void *fn, void *arg, const char *format, va_list va, int *wrote) {
         }
         break;
       }
+      case 'C':
+        signbit = 63;
+        // fallthrough
       case 'c':
         if ((charbuf[0] = va_arg(va, int))) {
           p = charbuf;
diff --git a/test/libc/stdio/snprintf_test.c b/test/libc/stdio/snprintf_test.c
index 21f4f5e06..6f7d895eb 100644
--- a/test/libc/stdio/snprintf_test.c
+++ b/test/libc/stdio/snprintf_test.c
@@ -71,3 +71,33 @@ TEST(snprintf, testInf) {
   for (i = 4; i < 10; ++i)
     ASSERT_EQ(buf[i], '\0');
 }
+
+TEST(snprintf, testUppercaseCConversionSpecifier) {
+  char buf[10] = {};
+  int i = snprintf(buf, sizeof(buf), "%C", L'a');
+
+  ASSERT_EQ(i, 1);
+  ASSERT_STREQ(buf, "a");
+
+  i = snprintf(buf, sizeof(buf), "%C", L'☺');
+  ASSERT_EQ(i, 3);
+  ASSERT_STREQ(buf, "☺");
+}
+
+// Make sure we don't va_arg the wrong argument size on wide character
+// conversion specifiers
+TEST(snprintf,
+     testWideCConversionSpecifierWithLotsOfArgumentsBeforeAndOneAfter) {
+  char buf[20] = {};
+  int i = snprintf(buf, sizeof(buf), "%d%d%d%d%d%d%d%d%lc%d", 0, 0, 0, 0, 0, 0,
+                   0, 0, L'x', 1);
+
+  ASSERT_EQ(i, 10);
+  ASSERT_STREQ(buf, "00000000x1");
+
+  memset(buf, 0, sizeof(buf));
+  i = snprintf(buf, sizeof(buf), "%d%d%d%d%d%d%d%d%C%d", 0, 0, 0, 0, 0, 0, 0, 0,
+               L'x', 1);
+  ASSERT_EQ(i, 10);
+  ASSERT_STREQ(buf, "00000000x1");
+}