diff --git a/abaplint.json b/abaplint.json
index e6bd22a..3352806 100644
--- a/abaplint.json
+++ b/abaplint.json
@@ -78,7 +78,7 @@
     "identical_conditions": true,
     "line_break_style": false,
     "many_parentheses": true,
-    "prefer_is_not": false,
+    "prefer_is_not": true,
     "unused_types": true,
     "use_bool_expression": false,
     "use_line_exists": false,
diff --git a/src/integer/zcl_abappgp_integer.clas.abap b/src/integer/zcl_abappgp_integer.clas.abap
index 8ac4aef..1ad1a41 100644
--- a/src/integer/zcl_abappgp_integer.clas.abap
+++ b/src/integer/zcl_abappgp_integer.clas.abap
@@ -752,7 +752,7 @@ CLASS zcl_abappgp_integer IMPLEMENTATION.
 
     ASSERT lv_str CO '-1234567890'.
     IF strlen( lv_str ) > 1.
-      ASSERT NOT lv_str(1) = '0'.
+      ASSERT lv_str(1) <> '0'.
     ENDIF.
 
     CREATE OBJECT ro_integer.
@@ -1001,7 +1001,7 @@ CLASS zcl_abappgp_integer IMPLEMENTATION.
           lo_mult TYPE REF TO zcl_abappgp_integer.
 
 
-    ASSERT NOT io_integer->mv_negative = abap_true.
+    ASSERT io_integer->mv_negative <> abap_true.
 
 * todo, new protected divide method that returns both quotient and remainder
     lo_div = clone( )->divide_knuth( io_integer ).
@@ -1022,7 +1022,7 @@ CLASS zcl_abappgp_integer IMPLEMENTATION.
           lo_exponent TYPE REF TO zcl_abappgp_binary_integer.
 
 
-    ASSERT NOT io_modulus->mv_negative = abap_true.
+    ASSERT io_modulus->mv_negative <> abap_true.
 
     IF io_modulus->is_one( ) = abap_true.
       split( '0' ).
@@ -1072,7 +1072,7 @@ CLASS zcl_abappgp_integer IMPLEMENTATION.
           lo_basem    TYPE REF TO zcl_abappgp_montgomery_integer.
 
 
-    ASSERT NOT io_modulus->mv_negative = abap_true.
+    ASSERT io_modulus->mv_negative <> abap_true.
 
     IF io_modulus->is_one( ) = abap_true.
       split( '0' ).
@@ -1384,7 +1384,7 @@ CLASS zcl_abappgp_integer IMPLEMENTATION.
           lo_original TYPE REF TO zcl_abappgp_integer.
 
 
-    ASSERT NOT io_integer->mv_negative = abap_true.
+    ASSERT io_integer->mv_negative <> abap_true.
 
     IF io_integer->is_zero( ) = abap_true.
       split( '1' ).
diff --git a/src/integer/zcl_abappgp_integer2.clas.abap b/src/integer/zcl_abappgp_integer2.clas.abap
index 714da9f..550d529 100644
--- a/src/integer/zcl_abappgp_integer2.clas.abap
+++ b/src/integer/zcl_abappgp_integer2.clas.abap
@@ -302,7 +302,7 @@ CLASS ZCL_ABAPPGP_INTEGER2 IMPLEMENTATION.
       lo_int->divide_by_2( ).
     ENDWHILE.
 
-    IF NOT lv_hex IS INITIAL.
+    IF lv_hex IS NOT INITIAL.
       lv_int = lv_hex.
       APPEND lv_int TO ro_integer->mt_split.
     ENDIF.
diff --git a/src/pgp/zabappgp_keys.prog.abap b/src/pgp/zabappgp_keys.prog.abap
index 56c93bd..7677320 100644
--- a/src/pgp/zabappgp_keys.prog.abap
+++ b/src/pgp/zabappgp_keys.prog.abap
@@ -260,7 +260,7 @@ CLASS lcl_key IMPLEMENTATION.
 
   METHOD init.
 
-    IF NOT go_cprivate IS BOUND.
+    IF go_cprivate IS NOT BOUND.
       CREATE OBJECT go_cprivate
         EXPORTING
           container_name = 'CUSTOM_PRIVATE'.
diff --git a/src/pgp/zcl_abappgp_armor.clas.abap b/src/pgp/zcl_abappgp_armor.clas.abap
index cddcdca..9d21303 100644
--- a/src/pgp/zcl_abappgp_armor.clas.abap
+++ b/src/pgp/zcl_abappgp_armor.clas.abap
@@ -66,9 +66,9 @@ CLASS zcl_abappgp_armor IMPLEMENTATION.
 
   METHOD constructor.
 
-    ASSERT NOT iv_armor_header IS INITIAL.
-    ASSERT NOT iv_data IS INITIAL.
-    ASSERT NOT iv_armor_tail IS INITIAL.
+    ASSERT iv_armor_header IS NOT INITIAL.
+    ASSERT iv_data IS NOT INITIAL.
+    ASSERT iv_armor_tail IS NOT INITIAL.
 
     mv_armor_header = iv_armor_header.
     mt_headers      = it_headers.
diff --git a/src/zabappgp_sign.prog.abap b/src/zabappgp_sign.prog.abap
index ef3ce2a..22074e2 100644
--- a/src/zabappgp_sign.prog.abap
+++ b/src/zabappgp_sign.prog.abap
@@ -36,7 +36,7 @@ CLASS lcl_screen_2000 IMPLEMENTATION.
     SET PF-STATUS 'STATUS_2000'.
     SET TITLEBAR 'TITLE_2000'.
 
-    IF NOT go_container1 IS BOUND.
+    IF go_container1 IS NOT BOUND.
       CREATE OBJECT go_container1
         EXPORTING
           container_name = 'CUSTOM_INPUT'.
diff --git a/src/zcl_abappgp_symmetric.clas.testclasses.abap b/src/zcl_abappgp_symmetric.clas.testclasses.abap
index 19e2de5..42f85c1 100644
--- a/src/zcl_abappgp_symmetric.clas.testclasses.abap
+++ b/src/zcl_abappgp_symmetric.clas.testclasses.abap
@@ -34,7 +34,7 @@ CLASS ltcl_aes256 IMPLEMENTATION.
       iv_ivector = c_ivector
       iv_resync  = iv_resync ).
 
-    IF NOT iv_exp IS INITIAL.
+    IF iv_exp IS NOT INITIAL.
       cl_abap_unit_assert=>assert_equals(
         act = lv_enc
         exp = iv_exp ).