diff --git a/mandel.s b/mandel.s
index 3579b0f..cf52fdb 100644
--- a/mandel.s
+++ b/mandel.s
@@ -107,7 +107,7 @@ KEY_RIGHT = $87
 
 .struct float48
     exponent .byte
-    mantissa .byte 6
+    mantissa .byte 5
 .endstruct
 
 .import mul_lobyte256