diff --git a/reactos/lib/sdk/crt/crt.rbuild b/reactos/lib/sdk/crt/crt.rbuild
index d9e31fa3ab0..de4b1748363 100644
--- a/reactos/lib/sdk/crt/crt.rbuild
+++ b/reactos/lib/sdk/crt/crt.rbuild
@@ -314,6 +314,7 @@
 		<file>assert.c</file>
 		<file>environ.c</file>
 		<file>getargs.c</file>
+		<file>i10output.c</file>
 		<file>initterm.c</file>
 		<file>lock.c</file>
 		<file>purecall.c</file>
diff --git a/reactos/lib/sdk/crt/misc/i10output.c b/reactos/lib/sdk/crt/misc/i10output.c
new file mode 100644
index 00000000000..779e2ab4cb0
--- /dev/null
+++ b/reactos/lib/sdk/crt/misc/i10output.c
@@ -0,0 +1,99 @@
+#include <precomp.h>
+
+#define I10_OUTPUT_MAX_PREC 21
+/* Internal structure used by $I10_OUTPUT */
+struct _I10_OUTPUT_DATA {
+    short pos;
+    char sign;
+    BYTE len;
+    char str[I10_OUTPUT_MAX_PREC+1]; /* add space for '\0' */
+};
+
+/*********************************************************************
+ *              $I10_OUTPUT (MSVCRT.@)
+ * ld - long double to be printed to data
+ * prec - precision of part, we're interested in
+ * flag - 0 for first prec digits, 1 for fractional part
+ * data - data to be populated
+ *
+ * return value
+ *      0 if given double is NaN or INF
+ *      1 otherwise
+ *
+ * FIXME
+ *      Native sets last byte of data->str to '0' or '9', I don't know what
+ *      it means. Current implementation sets it always to '0'.
+ */
+int CDECL MSVCRT_I10_OUTPUT(long double ld, int prec, int flag, struct _I10_OUTPUT_DATA *data)
+{
+    static const char inf_str[] = "1#INF";
+    static const char nan_str[] = "1#QNAN";
+
+    double d = ld;
+    char format[8];
+    char buf[I10_OUTPUT_MAX_PREC+9]; /* 9 = strlen("0.e+0000") + '\0' */
+    char *p;
+
+    TRACE("(%lf %d %x %p)\n", d, prec, flag, data);
+
+    if(d<0) {
+        data->sign = '-';
+        d = -d;
+    } else
+        data->sign = ' ';
+
+    if(isinf(d)) {
+        data->pos = 1;
+        data->len = 5;
+        memcpy(data->str, inf_str, sizeof(inf_str));
+
+        return 0;
+    }
+
+    if(isnan(d)) {
+        data->pos = 1;
+        data->len = 6;
+        memcpy(data->str, nan_str, sizeof(nan_str));
+
+        return 0;
+    }
+
+    if(flag&1) {
+        int exp = 1+floor(log10(d));
+
+        prec += exp;
+        if(exp < 0)
+            prec--;
+    }
+    prec--;
+
+    if(prec+1 > I10_OUTPUT_MAX_PREC)
+        prec = I10_OUTPUT_MAX_PREC-1;
+    else if(prec < 0) {
+        d = 0.0;
+        prec = 0;
+    }
+
+    sprintf(format, "%%.%dle", prec);
+    sprintf(buf, format, d);
+
+    buf[1] = buf[0];
+    data->pos = atoi(buf+prec+3);
+    if(buf[1] != '0')
+        data->pos++;
+
+    for(p = buf+prec+1; p>buf+1 && *p=='0'; p--);
+    data->len = p-buf;
+
+    memcpy(data->str, buf+1, data->len);
+    data->str[data->len] = '\0';
+
+    if(buf[1]!='0' && prec-data->len+1>0)
+        memcpy(data->str+data->len+1, buf+data->len+1, prec-data->len+1);
+
+    return 1;
+}
+#undef I10_OUTPUT_MAX_PREC
+
+
+
diff --git a/reactos/lib/sdk/crt/misc/stubs.c b/reactos/lib/sdk/crt/misc/stubs.c
index 7eac2b0fef9..98641dc83a1 100644
--- a/reactos/lib/sdk/crt/misc/stubs.c
+++ b/reactos/lib/sdk/crt/misc/stubs.c
@@ -6,15 +6,6 @@ int __STRINGTOLD( long double *value, char **endptr, const char *str, int flags
    return 0;
 }
 
-/*********************************************************************
- *		$I10_OUTPUT (MSVCRT.@)
- * Function not really understood but needed to make the DLL work
- */
-void MSVCRT_I10_OUTPUT(void)
-{
-  /* FIXME: This is probably data, not a function */
-}
-
 void __fileinfo(void)
 {
    FIXME("__fileinfo stub\n");