diff --git a/fpu/softfloat.c b/fpu/softfloat.c
index 8413146..62830d7 100644
--- a/fpu/softfloat.c
+++ b/fpu/softfloat.c
@@ -1273,9 +1273,14 @@ float64 int64_to_float64( int64 a STATUS_PARAM )
 
 float64 uint64_to_float64( uint64 a STATUS_PARAM )
 {
-    if ( a == 0 ) return float64_zero;
-    return normalizeRoundAndPackFloat64( 0, 0x43C, a STATUS_VAR );
+    int exp =  0x43C;
 
+    if ( a == 0 ) return float64_zero;
+    if ( (int64_t)a < 0 ) {
+        shift64RightJamming(a, 1, &a);
+        exp += 1;
+    }
+    return normalizeRoundAndPackFloat64( 0, exp, a STATUS_VAR );
 }
 
 /*----------------------------------------------------------------------------