diff --git a/tests/extern.data32 b/tests/extern.data32
index 60d155d..0031643 100644
Binary files a/tests/extern.data32 and b/tests/extern.data32 differ
diff --git a/tests/extern.data64 b/tests/extern.data64
index 096750b..6d0c104 100644
Binary files a/tests/extern.data64 and b/tests/extern.data64 differ
diff --git a/tests/extern.ml b/tests/extern.ml
index 33819a8..247677b 100644
--- a/tests/extern.ml
+++ b/tests/extern.ml
@@ -3,12 +3,12 @@
 let _ =
   let file = Sys.argv.(1) in
   let oc = open_out_bin file in
-  for nbits = 2 to 128 do
+  for nbits = 16 to 128 do
     let x = Z.shift_left Z.one nbits in
-    output_value oc x;
-    output_value oc (Z.pred x);
+    output_value oc (Z.pred (Z.neg x));
     output_value oc (Z.neg x);
-    output_value oc (Z.neg (Z.pred x))
+    output_value oc (Z.pred x);
+    output_value oc x
   done;
   close_out oc
 
diff --git a/tests/intern.ml b/tests/intern.ml
index cd359c2..c7940ae 100644
--- a/tests/intern.ml
+++ b/tests/intern.ml
@@ -12,13 +12,13 @@ let expect ic n =
 let _ =
   let file = Sys.argv.(1) in
   let ic = open_in_bin file in
-  for nbits = 2 to 128 do
+  for nbits = 16 to 128 do
     printf "%d:" nbits;
     let x = Z.shift_left Z.one nbits in
-    expect ic x;
-    expect ic (Z.pred x);
+    expect ic (Z.pred (Z.neg x));
     expect ic (Z.neg x);
-    expect ic (Z.neg (Z.pred x));
+    expect ic (Z.pred x);
+    expect ic x;
     print_newline()
   done;
   close_in ic
diff --git a/tests/intern.output3232 b/tests/intern.output3232
index b2c34a1..9029dd2 100644
--- a/tests/intern.output3232
+++ b/tests/intern.output3232
@@ -1,17 +1,3 @@
-2: OK OK OK OK
-3: OK OK OK OK
-4: OK OK OK OK
-5: OK OK OK OK
-6: OK OK OK OK
-7: OK OK OK OK
-8: OK OK OK OK
-9: OK OK OK OK
-10: OK OK OK OK
-11: OK OK OK OK
-12: OK OK OK OK
-13: OK OK OK OK
-14: OK OK OK OK
-15: OK OK OK OK
 16: OK OK OK OK
 17: OK OK OK OK
 18: OK OK OK OK
diff --git a/tests/intern.output3264 b/tests/intern.output3264
index 5327d0a..bcacdfb 100644
--- a/tests/intern.output3264
+++ b/tests/intern.output3264
@@ -1,17 +1,3 @@
-2: OK OK OK OK
-3: OK OK OK OK
-4: OK OK OK OK
-5: OK OK OK OK
-6: OK OK OK OK
-7: OK OK OK OK
-8: OK OK OK OK
-9: OK OK OK OK
-10: OK OK OK OK
-11: OK OK OK OK
-12: OK OK OK OK
-13: OK OK OK OK
-14: OK OK OK OK
-15: OK OK OK OK
 16: OK OK OK OK
 17: OK OK OK OK
 18: OK OK OK OK
@@ -26,7 +12,7 @@
 27: OK OK OK OK
 28: OK OK OK OK
 29: OK OK OK OK
-30: Fail OK OK OK
+30: Fail OK OK Fail
 31: Fail Fail Fail Fail
 32: Fail Fail Fail Fail
 33: Fail Fail Fail Fail
@@ -58,7 +44,7 @@
 59: Fail Fail Fail Fail
 60: Fail Fail Fail Fail
 61: Fail Fail Fail Fail
-62: OK Fail Fail Fail
+62: OK Fail Fail OK
 63: OK OK OK OK
 64: OK OK OK OK
 65: OK OK OK OK
diff --git a/tests/intern.output6432 b/tests/intern.output6432
index 5327d0a..bcacdfb 100644
--- a/tests/intern.output6432
+++ b/tests/intern.output6432
@@ -1,17 +1,3 @@
-2: OK OK OK OK
-3: OK OK OK OK
-4: OK OK OK OK
-5: OK OK OK OK
-6: OK OK OK OK
-7: OK OK OK OK
-8: OK OK OK OK
-9: OK OK OK OK
-10: OK OK OK OK
-11: OK OK OK OK
-12: OK OK OK OK
-13: OK OK OK OK
-14: OK OK OK OK
-15: OK OK OK OK
 16: OK OK OK OK
 17: OK OK OK OK
 18: OK OK OK OK
@@ -26,7 +12,7 @@
 27: OK OK OK OK
 28: OK OK OK OK
 29: OK OK OK OK
-30: Fail OK OK OK
+30: Fail OK OK Fail
 31: Fail Fail Fail Fail
 32: Fail Fail Fail Fail
 33: Fail Fail Fail Fail
@@ -58,7 +44,7 @@
 59: Fail Fail Fail Fail
 60: Fail Fail Fail Fail
 61: Fail Fail Fail Fail
-62: OK Fail Fail Fail
+62: OK Fail Fail OK
 63: OK OK OK OK
 64: OK OK OK OK
 65: OK OK OK OK
diff --git a/tests/intern.output6464 b/tests/intern.output6464
index b2c34a1..9029dd2 100644
--- a/tests/intern.output6464
+++ b/tests/intern.output6464
@@ -1,17 +1,3 @@
-2: OK OK OK OK
-3: OK OK OK OK
-4: OK OK OK OK
-5: OK OK OK OK
-6: OK OK OK OK
-7: OK OK OK OK
-8: OK OK OK OK
-9: OK OK OK OK
-10: OK OK OK OK
-11: OK OK OK OK
-12: OK OK OK OK
-13: OK OK OK OK
-14: OK OK OK OK
-15: OK OK OK OK
 16: OK OK OK OK
 17: OK OK OK OK
 18: OK OK OK OK