diff --git a/config/suppressions.xml b/config/suppressions.xml
index a8e939695..07d2bc0e2 100644
--- a/config/suppressions.xml
+++ b/config/suppressions.xml
@@ -63,9 +63,6 @@
     <suppress checks="." files=".*JavadocTokenTypes\.java"/>
     <suppress checks="." files=".*ParseTreeBuilder\.java"/>
 
-    <!-- Should be solved after fixing https://github.com/checkstyle/checkstyle/issues/1805 -->
-    <suppress checks="IllegalType" files=".*[\\/]src[\\/]test[\\/]|(AbstractTypeAwareCheck|TryHandler|SlistHandler|PrimordialHandler|MethodCallHandler|MemberDefHandler|IndentationCheck|IfHandler|HandlerFactory|CaseHandler|BlockParentHandler|AbstractExpressionHandler|JavadocMethodCheck|DetectorOptions)\.java"/>
-
     <!-- Till https://github.com/checkstyle/checkstyle/issues/1854 -->
     <suppress checks="TrailingComment" files="(InnerAssignmentCheck\.java|OperatorWrapCheck\.java|XMLLoggerTest\.java|AbbreviationAsWordInNameCheckTest\.java)"/>
 
diff --git a/src/test/java/com/puppycrawl/tools/checkstyle/CheckerTest.java b/src/test/java/com/puppycrawl/tools/checkstyle/CheckerTest.java
index 22263e5c6..0c318970c 100644
--- a/src/test/java/com/puppycrawl/tools/checkstyle/CheckerTest.java
+++ b/src/test/java/com/puppycrawl/tools/checkstyle/CheckerTest.java
@@ -29,7 +29,7 @@ import java.io.UnsupportedEncodingException;
 import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.List;
-import java.util.TreeSet;
+import java.util.SortedSet;
 
 import org.junit.Test;
 
@@ -56,7 +56,7 @@ public class CheckerTest {
         checker.fireFileStarted("Some File Name");
         checker.fireFileFinished("Some File Name");
 
-        final TreeSet<LocalizedMessage> msgs = Sets.newTreeSet();
+        final SortedSet<LocalizedMessage> msgs = Sets.newTreeSet();
         msgs.add(new LocalizedMessage(0, 0, "a Bundle", "message.key",
                 new Object[] {"arg"}, null, getClass(), null));
         checker.fireErrors("Some File Name", msgs);
@@ -88,7 +88,7 @@ public class CheckerTest {
         assertTrue("Checker.fireFileFinished() doesn't call listener", auditAdapter.wasCalled());
 
         auditAdapter.resetListener();
-        final TreeSet<LocalizedMessage> msgs = Sets.newTreeSet();
+        final SortedSet<LocalizedMessage> msgs = Sets.newTreeSet();
         msgs.add(new LocalizedMessage(0, 0, "a Bundle", "message.key",
                 new Object[] {"arg"}, null, getClass(), null));
         checker.fireErrors("Some File Name", msgs);
@@ -125,7 +125,7 @@ public class CheckerTest {
         assertFalse("Checker.fireFileFinished() does call removed listener", auditAdapter.wasCalled());
 
         aa2.resetListener();
-        final TreeSet<LocalizedMessage> msgs = Sets.newTreeSet();
+        final SortedSet<LocalizedMessage> msgs = Sets.newTreeSet();
         msgs.add(new LocalizedMessage(0, 0, "a Bundle", "message.key",
                 new Object[] {"arg"}, null, getClass(), null));
         checker.fireErrors("Some File Name", msgs);
@@ -142,7 +142,7 @@ public class CheckerTest {
         checker.addFilter(filter);
 
         filter.resetFilter();
-        final TreeSet<LocalizedMessage> msgs = Sets.newTreeSet();
+        final SortedSet<LocalizedMessage> msgs = Sets.newTreeSet();
         msgs.add(new LocalizedMessage(0, 0, "a Bundle", "message.key",
                 new Object[] {"arg"}, null, getClass(), null));
         checker.fireErrors("Some File Name", msgs);
@@ -159,7 +159,7 @@ public class CheckerTest {
         checker.removeFilter(filter);
 
         f2.resetFilter();
-        final TreeSet<LocalizedMessage> msgs = Sets.newTreeSet();
+        final SortedSet<LocalizedMessage> msgs = Sets.newTreeSet();
         msgs.add(new LocalizedMessage(0, 0, "a Bundle", "message.key",
                 new Object[] {"arg"}, null, getClass(), null));
         checker.fireErrors("Some File Name", msgs);
diff --git a/src/test/java/com/puppycrawl/tools/checkstyle/PackageNamesLoaderTest.java b/src/test/java/com/puppycrawl/tools/checkstyle/PackageNamesLoaderTest.java
index 305b88c70..a3efad0a2 100644
--- a/src/test/java/com/puppycrawl/tools/checkstyle/PackageNamesLoaderTest.java
+++ b/src/test/java/com/puppycrawl/tools/checkstyle/PackageNamesLoaderTest.java
@@ -36,7 +36,6 @@ import java.net.URLConnection;
 import java.net.URLStreamHandler;
 import java.util.Arrays;
 import java.util.Enumeration;
-import java.util.LinkedHashSet;
 import java.util.Set;
 
 import org.junit.Test;
@@ -106,7 +105,7 @@ public class PackageNamesLoaderTest {
 
         Field field = PackageNamesLoader.class.getDeclaredField("packageNames");
         field.setAccessible(true);
-        LinkedHashSet<String> list = (LinkedHashSet<String>) field.get(loader);
+        Set<String> list = (Set<String>) field.get(loader);
         assertEquals("coding.", list.iterator().next());
     }