diff --git a/java/java-impl/src/com/intellij/codeInsight/annoPackages/JetBrainsAnnotationSupport.java b/java/java-impl/src/com/intellij/codeInsight/annoPackages/JetBrainsAnnotationSupport.java
index 709b4e325649..1d961d0fa9f6 100644
--- a/java/java-impl/src/com/intellij/codeInsight/annoPackages/JetBrainsAnnotationSupport.java
+++ b/java/java-impl/src/com/intellij/codeInsight/annoPackages/JetBrainsAnnotationSupport.java
@@ -17,8 +17,10 @@ class JetBrainsAnnotationSupport implements AnnotationPackageSupport {
         return Collections.singletonList(AnnotationUtil.NOT_NULL);
       case NULLABLE:
         return Collections.singletonList(AnnotationUtil.NULLABLE);
+      case UNKNOWN:
+        return Collections.singletonList(AnnotationUtil.UNKNOWN_NULLABILITY);
       default:
-        return Collections.emptyList();
+        throw new IllegalStateException("Unexpected value: " + nullability);
     }
   }
 }
diff --git a/java/java-psi-api/src/com/intellij/codeInsight/AnnotationUtil.java b/java/java-psi-api/src/com/intellij/codeInsight/AnnotationUtil.java
index 2548e8396136..589e3ce3b619 100644
--- a/java/java-psi-api/src/com/intellij/codeInsight/AnnotationUtil.java
+++ b/java/java-psi-api/src/com/intellij/codeInsight/AnnotationUtil.java
@@ -21,6 +21,7 @@ import java.util.stream.Stream;
 @ApiStatus.NonExtendable
 public class AnnotationUtil {
   public static final String NULLABLE = "org.jetbrains.annotations.Nullable";
+  public static final String UNKNOWN_NULLABILITY = "org.jetbrains.annotations.UnknownNullability";
   public static final String NOT_NULL = "org.jetbrains.annotations.NotNull";
 
   public static final String NON_NLS = "org.jetbrains.annotations.NonNls";
@@ -220,7 +221,7 @@ public class AnnotationUtil {
     AnnotationAndOwner result = findAnnotationAndOwnerInHierarchy(listOwner, annotationNames, skipExternal);
     return result == null ? null : result.annotation;
   }
-  
+
   static final class AnnotationAndOwner {
     final @NotNull PsiModifierListOwner owner;
     final @NotNull PsiAnnotation annotation;
diff --git a/java/java-tests/testData/inspection/dataFlow/fixture/UnknownNullability.java b/java/java-tests/testData/inspection/dataFlow/fixture/UnknownNullability.java
new file mode 100644
index 000000000000..a7cf27bee070
--- /dev/null
+++ b/java/java-tests/testData/inspection/dataFlow/fixture/UnknownNullability.java
@@ -0,0 +1,33 @@
+import org.jetbrains.annotations.*;
+
+class UnknownNullabilityTest {
+  static final String getString() {
+    return "foo";
+  }
+
+  static final @UnknownNullability String getString2() {
+    return "foo";
+  }
+
+  static final String getStringNullable() {
+    return Math.random() > 0.5 ? "foo" : null;
+  }
+
+  static final @UnknownNullability String getStringNullable2() {
+    return Math.random() > 0.5 ? "foo" : null;
+  }
+
+  void check() {
+    if (<warning descr="Condition 'getString() == null' is always 'false'">getString() == null</warning>) {}
+    if (getString2() == null) {}
+    if (getStringNullable() == null) {}
+    if (getStringNullable2() == null) {}
+  }
+
+  void deref() {
+    if (Math.random() > 0.5) getString().trim();
+    if (Math.random() > 0.5) getString2().trim();
+    if (Math.random() > 0.5) getStringNullable().<warning descr="Method invocation 'trim' may produce 'NullPointerException'">trim</warning>();
+    if (Math.random() > 0.5) getStringNullable2().trim();
+  }
+}
\ No newline at end of file
diff --git a/java/java-tests/testSrc/com/intellij/java/codeInspection/DataFlowInspection8Test.java b/java/java-tests/testSrc/com/intellij/java/codeInspection/DataFlowInspection8Test.java
index bba90e726bf2..95f0ecd5b438 100644
--- a/java/java-tests/testSrc/com/intellij/java/codeInspection/DataFlowInspection8Test.java
+++ b/java/java-tests/testSrc/com/intellij/java/codeInspection/DataFlowInspection8Test.java
@@ -188,7 +188,7 @@ public class DataFlowInspection8Test extends DataFlowInspectionTestCase {
   public void testStreamInlining() { doTest(); }
   public void testStreamCollectInlining() {
     setupTypeUseAnnotations("foo", myFixture);
-    doTest(); 
+    doTest();
   }
   public void testStreamCollectorInlining() { doTest(); }
   public void testStreamToMapInlining() { doTest(); }
@@ -203,7 +203,7 @@ public class DataFlowInspection8Test extends DataFlowInspectionTestCase {
   public void testStreamAnyMatchIsNull() { doTest(); }
   public void testStreamCustomSumMethod() { doTest(); }
   public void testStreamReduceLogicalAnd() { doTest(); }
-  
+
   public void testMapGetWithValueNullability() { doTestWithCustomAnnotations(); }
   public void testInferNestedForeachNullability() { doTestWithCustomAnnotations(); }
 
@@ -251,7 +251,7 @@ public class DataFlowInspection8Test extends DataFlowInspectionTestCase {
     doTest();
   }
 
-  public void testConflictsInInferredTypes() { 
+  public void testConflictsInInferredTypes() {
     setupAmbiguousAnnotations("foo", myFixture);
     doTest();
   }
@@ -330,4 +330,10 @@ public class DataFlowInspection8Test extends DataFlowInspectionTestCase {
     doTest();
   }
   public void testConstantInClosure() { doTest(); }
+  public void testUnknownNullability() {
+    myFixture.addClass("package org.jetbrains.annotations;\nimport java.lang.annotation.*;\n" +
+                       "@Target(ElementType.TYPE_USE)\n" +
+                       "public @interface UnknownNullability { }");
+    doTestWith(insp -> insp.SUGGEST_NULLABLE_ANNOTATIONS = false);
+  }
 }
\ No newline at end of file