diff --git a/FrontEnd/Lib/bytestream.cw b/FrontEnd/Lib/bytestream.cw
index 8f0f970f..77e8b32f 100644
--- a/FrontEnd/Lib/bytestream.cw
+++ b/FrontEnd/Lib/bytestream.cw
@@ -42,6 +42,10 @@
 (fun @pub FrontSlice [
     (param buffer (ptr @mut (slice u8))) (param n uint)]
             (union [(slice u8) OutOfBoundsError]) :
+    (if (<= (len  (^ buffer)) n) :
+        (return OutOfBoundsErrorVal)
+    :)
+
     (let out (slice u8) (slice_val (front (^ buffer)) n))
     (stmt (IncSliceUnchecked [buffer n]))
     (return out)
diff --git a/FrontEnd/Lib/bytestream_test.cw b/FrontEnd/Lib/bytestream_test.cw
index 849d6517..36c57dcb 100644
--- a/FrontEnd/Lib/bytestream_test.cw
+++ b/FrontEnd/Lib/bytestream_test.cw
@@ -3,20 +3,76 @@
 (import test)
 (import bytestream)
 
-(fun test_all [] void :
-    @doc "(test::AssertSliceEq! )"
+
+(fun test_bs_or_die [] void :
     (let @mut data (array 23 u8) "\x22\x33\x44\x55\x66\x77\x88abcdefghijklmnop")
     (let @mut @ref stream (slice u8) data)
-     (test::AssertEq! 0x22_u8
+    (test::AssertEq! 0x22_u8
                       (bytestream::FrontLeU8OrDie [(& @mut stream)]))
     (test::AssertEq! 0x4433_u16
                       (bytestream::FrontLeU16OrDie [(& @mut stream)]))
     (test::AssertEq! 0x88776655_u32
                       (bytestream::FrontLeU32OrDie [(& @mut stream)]))
+
+    (test::AssertSliceEq!
+         (bytestream::FrontSliceOrDie [(& @mut stream) 10])
+          "abcdefghij")
+    (test::AssertSliceEq!
+         (bytestream::FrontSliceOrDie [(& @mut stream) 1])
+          "k")
+    (let empty_slice (slice u8))
+    (test::AssertSliceEq!
+         (bytestream::FrontSliceOrDie [(& @mut stream) 0])
+         empty_slice)
+)
+
+(fun test_bs [] void :
+    (let @mut data (array 23 u8) "\x22\x33\x44\x55\x66\x77\x88abcdefghijklmnop")
+    (let @mut @ref stream (slice u8) data)
+    (test::AssertEq! 0x22_u8
+                      (bytestream::FrontLeU8 [(& @mut stream)]))
+    (test::AssertEq! 0x4433_u16
+                      (bytestream::FrontLeU16 [(& @mut stream)]))
+    (test::AssertEq! 0x88776655_u32
+                      (bytestream::FrontLeU32 [(& @mut stream)]))
+
+    (let raw1 auto  (bytestream::FrontSlice [(& @mut stream) 10]))
+    (let dummy1 auto (typeid  (slice u8)))
+    (let dummy2 auto (typeid  bytestream::OutOfBoundsError))
+
+    (try result1 (slice u8) raw1 err :
+        (test::AssertUnreachable!)
+    )
+    (test::AssertSliceEq! result1 "abcdefghij")
+
+
+    (let raw2 auto  (bytestream::FrontSlice [(& @mut stream) 1000]))
+    (try result2  bytestream::OutOfBoundsError raw2 err :
+        (test::AssertUnreachable!)
+    )
+
+    (let raw3 auto  (bytestream::FrontSlice [(& @mut stream) 1]))
+    (try result3 (slice u8) raw3 err :
+        (test::AssertUnreachable!)
+    )
+    (test::AssertSliceEq! result3 "k")
+
+    (let raw4 auto  (bytestream::FrontSlice [(& @mut stream) 1000]))
+    (try result4  bytestream::OutOfBoundsError raw4 err :
+        (test::AssertUnreachable!)
+    )
+
+    (let empty_slice (slice u8))
+    (let raw5 auto  (bytestream::FrontSlice [(& @mut stream) 0]))
+    (try result5 (slice u8) raw5 err :
+        (test::AssertUnreachable!)
+    )
+    (test::AssertSliceEq! result5 empty_slice)
 )
 
 (fun @cdecl main [(param argc s32) (param argv (ptr (ptr u8)))] s32 :
-    (stmt (test_all []))
+    (stmt (test_bs_or_die []))
+    (stmt (test_bs []))
 
     @doc "test end"
     (test::Success!)
diff --git a/FrontEnd/Lib/test.cw b/FrontEnd/Lib/test.cw
index 654f46c8..3a978119 100644
--- a/FrontEnd/Lib/test.cw
+++ b/FrontEnd/Lib/test.cw
@@ -84,7 +84,7 @@ Both must have derivable types as we use `auto`"""
     $epsilon)
 
 @doc ""
-(macro @pub AssertTrue! STMT_LIST [(mparam $e_expr EXPR)] [$e_val $a_val] :
+(macro @pub AssertTrue! STMT_LIST [(mparam $e_expr EXPR)] [] :
     (if  $e_expr : :
         (SysPrint! "AssertTrue failed: ")
         (SysPrint! (stringify $e_expr))
@@ -93,7 +93,7 @@ Both must have derivable types as we use `auto`"""
         ))
 
 @doc ""
-(macro @pub AssertFalse! STMT_LIST [(mparam $e_expr EXPR)] [$e_val $a_val] :
+(macro @pub AssertFalse! STMT_LIST [(mparam $e_expr EXPR)] [] :
     (if  $e_expr :
         (SysPrint! "AssertFalse failed: ")
         (SysPrint! (stringify $e_expr))
@@ -101,4 +101,10 @@ Both must have derivable types as we use `auto`"""
         (trap)
         : ))
 
+@doc ""
+(macro @pub AssertUnreachable! STMT_LIST [] [] :
+    (SysPrint! "AssertUnreachable\n")
+    (trap)
+)
+
 )