diff --git a/jre_emul/Classes/FastPointerLookup.h b/jre_emul/Classes/FastPointerLookup.h
index d22c58fd13..1a3b7ad599 100644
--- a/jre_emul/Classes/FastPointerLookup.h
+++ b/jre_emul/Classes/FastPointerLookup.h
@@ -13,9 +13,12 @@
 #ifndef FastPointerLookup_H_
 #define FastPointerLookup_H_
 
+#import <Foundation/Foundation.h>
 #import <pthread.h>
 #import <stdbool.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 struct FastPointerLookupStore;
 
 typedef struct FastPointerLookup_t {
@@ -44,4 +47,5 @@ void *FastPointerLookup(FastPointerLookup_t *lookup, void *key);
 // new mapping was added, false if the key is already mapped.
 bool FastPointerLookupAddMapping(FastPointerLookup_t *lookup, void *key, void *value);
 
+NS_ASSUME_NONNULL_END
 #endif // FastPointerLookup_H_
diff --git a/jre_emul/Classes/IOSArray.h b/jre_emul/Classes/IOSArray.h
index 836ebe2a51..871d15a9f7 100644
--- a/jre_emul/Classes/IOSArray.h
+++ b/jre_emul/Classes/IOSArray.h
@@ -29,6 +29,7 @@
  * An abstract class that represents a Java array.  Like a Java array,
  * an IOSArray is fixed-size but its elements are mutable.
  */
+NS_ASSUME_NONNULL_BEGIN
 @interface IOSArray<__covariant ObjectType> : NSMutableArray<ObjectType> {
  @public
   /**
@@ -59,6 +60,7 @@
 - (void *)buffer;
 
 @end
+NS_ASSUME_NONNULL_END
 
 CF_EXTERN_C_BEGIN
 void IOSArray_throwOutOfBoundsWithMsg(jint size, jint index);
diff --git a/jre_emul/Classes/IOSArrayClass.h b/jre_emul/Classes/IOSArrayClass.h
index 8e11747afb..0aaec01c2f 100644
--- a/jre_emul/Classes/IOSArrayClass.h
+++ b/jre_emul/Classes/IOSArrayClass.h
@@ -26,10 +26,10 @@
 
 @interface IOSArrayClass : IOSClass {
   // An IOSClass is used instead of a Class so a IOSPrimitiveClass can be used.
-  IOSClass *componentType_;
+  IOSClass *_Nonnull componentType_;
 }
 
-- (instancetype)initWithComponentType:(IOSClass *)type;
+- (instancetype)initWithComponentType:(nonnull IOSClass *)type;
 
 @end
 
diff --git a/jre_emul/Classes/IOSClass.h b/jre_emul/Classes/IOSClass.h
index aadf532eda..712b8c0df5 100644
--- a/jre_emul/Classes/IOSClass.h
+++ b/jre_emul/Classes/IOSClass.h
@@ -45,6 +45,7 @@
  * instances: those representing real classes and interfaces, those
  * representing primitive types, and those representing array classes.
  */
+NS_ASSUME_NONNULL_BEGIN
 @interface IOSClass : NSObject <JavaLangReflectAnnotatedElement,
     JavaLangReflectGenericDeclaration, JavaIoSerializable,
     JavaLangReflectType, NSCopying> {
@@ -99,17 +100,17 @@
 
 // Class.getMethod(String, Class...)
 - (JavaLangReflectMethod *)getMethod:(NSString *)name
-                      parameterTypes:(IOSObjectArray *)types;
+                      parameterTypes:(nullable IOSObjectArray *)types;
 
 // Class.getDeclaredMethod(String, Class...)
 - (JavaLangReflectMethod *)getDeclaredMethod:(NSString *)name
-                              parameterTypes:(IOSObjectArray *)types;
+                              parameterTypes:(nullable IOSObjectArray *)types;
 
 // Class.getDeclaredConstructor(Class...)
-- (JavaLangReflectConstructor *)getDeclaredConstructor:(IOSObjectArray *)types;
+- (JavaLangReflectConstructor *)getDeclaredConstructor:(nullable IOSObjectArray *)types;
 
 // Class.getConstructor(Class)
-- (JavaLangReflectConstructor *)getConstructor:(IOSObjectArray *)types;
+- (JavaLangReflectConstructor *)getConstructor:(nullable IOSObjectArray *)types;
 
 // Class.getConstructors()
 - (IOSObjectArray *)getConstructors;
@@ -130,10 +131,10 @@
 + (IOSClass *)forName:(NSString *)className;
 + (IOSClass *)forName:(NSString *)className
            initialize:(jboolean)load
-          classLoader:(JavaLangClassLoader *)loader;
+          classLoader:(nullable JavaLangClassLoader *)loader;
 
 // Class.cast(Object)
-- (id)cast:(id)throwable;
+- (id)cast:(nullable id)throwable;
 
 // Class.getEnclosingClass()
 - (IOSClass *)getEnclosingClass;
@@ -154,9 +155,8 @@
 - (IOSObjectArray *)getGenericInterfaces;
 - (IOSObjectArray *)getTypeParameters;
 
-- (id<JavaLangAnnotationAnnotation>)
-      getAnnotationWithIOSClass:(IOSClass *)annotationClass;
-- (jboolean)isAnnotationPresentWithIOSClass:(IOSClass *)annotationType;
+- (id<JavaLangAnnotationAnnotation>)getAnnotationWithIOSClass:(nullable IOSClass *)annotationClass;
+- (jboolean)isAnnotationPresentWithIOSClass:(nullable IOSClass *)annotationType;
 - (IOSObjectArray *)getAnnotations;
 - (IOSObjectArray *)getDeclaredAnnotations;
 - (id<JavaLangAnnotationAnnotation>)
@@ -219,7 +219,7 @@ CF_EXTERN_C_BEGIN
 IOSClass *IOSClass_forName_(NSString *className);
 // Class.forName(String, boolean, ClassLoader)
 IOSClass *IOSClass_forName_initialize_classLoader_(
-    NSString *className, jboolean load, JavaLangClassLoader *loader);
+    NSString *className, jboolean load, JavaLangClassLoader * _Nullable loader);
 
 // Lookup a IOSClass from its associated ObjC class, protocol or component type.
 IOSClass *IOSClass_fromClass(Class cls);
@@ -252,4 +252,6 @@ J2OBJC_STATIC_INIT(IOSClass)
 
 J2OBJC_TYPE_LITERAL_HEADER(IOSClass)
 
+NS_ASSUME_NONNULL_END
+
 #endif // _IOSClass_H_
diff --git a/jre_emul/Classes/IOSConcreteClass.h b/jre_emul/Classes/IOSConcreteClass.h
index a64d98f7d6..4d170f13ff 100644
--- a/jre_emul/Classes/IOSConcreteClass.h
+++ b/jre_emul/Classes/IOSConcreteClass.h
@@ -24,12 +24,12 @@
 #import "IOSMetadata.h"
 
 @interface IOSConcreteClass : IOSClass {
-  Class class_;
+  Class _Nonnull class_;
 }
 
-- (instancetype)initWithClass:(Class)cls
-                     metadata:(const J2ObjcClassInfo *)metadata;
-- (instancetype)initWithClass:(Class)cls;
+- (instancetype)initWithClass:(Class _Nonnull)cls
+                     metadata:(const J2ObjcClassInfo * _Nonnull)metadata;
+- (instancetype)initWithClass:(Class _Nonnull)cls;
 
 @end
 
diff --git a/jre_emul/Classes/IOSPrimitiveArray.h b/jre_emul/Classes/IOSPrimitiveArray.h
index 877ffe7013..4d79c65def 100644
--- a/jre_emul/Classes/IOSPrimitiveArray.h
+++ b/jre_emul/Classes/IOSPrimitiveArray.h
@@ -47,6 +47,8 @@
 
 // ********** IOSBooleanArray **********
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  * An Objective-C representation of a Java boolean array. Like a Java array,
  * an IOSBooleanArray is fixed-size but its elements are mutable.
@@ -292,7 +294,7 @@ __attribute__((always_inline)) inline jchar *IOSCharArray_GetRef(
 - (void)getBytes:(jbyte *)buffer length:(NSUInteger)length;
 
 // Create an array from an NSData object.
-+ (instancetype)arrayWithNSData:(NSData *)data;
++ (instancetype)arrayWithNSData:(nullable NSData *)data;
 
 // Copies the array contents into a specified buffer, up to the specified
 // length.  An IndexOutOfBoundsException is thrown if the specified length
@@ -774,9 +776,8 @@ __attribute__((always_inline)) inline jdouble *IOSDoubleArray_GetRef(
   return &array->buffer_[index];
 }
 
+NS_ASSUME_NONNULL_END
 
-#undef PRIMITIVE_ARRAY_INTERFACE
-#undef PRIMITIVE_ARRAY_C_INTERFACE
+#pragma clang diagnostic pop // ignored "-Wzero-length-array"
 
-#pragma clang diagnostic pop
 #endif // IOSPrimitiveArray_H
diff --git a/jre_emul/Classes/IOSPrimitiveClass.h b/jre_emul/Classes/IOSPrimitiveClass.h
index 9d2a451d52..833e344960 100644
--- a/jre_emul/Classes/IOSPrimitiveClass.h
+++ b/jre_emul/Classes/IOSPrimitiveClass.h
@@ -28,14 +28,14 @@
 // be used with Java reflection routines.  This class is minimal because Java
 // primitive types have/need little runtime support, other than their name.
 @interface IOSPrimitiveClass : IOSClass {
-  NSString *name_;
-  NSString *type_;
+  NSString * _Nonnull name_;
+  NSString * _Nonnull type_;
 }
 
-- (instancetype)initWithName:(NSString *)name type:(NSString *)type;
+- (instancetype)initWithName:(NSString * _Nonnull)name type:(NSString * _Nonnull)type;
 
 // For a primitive type, return its associated wrapper class.
-- (IOSClass *)wrapperClass;
+- (IOSClass * _Nonnull)wrapperClass;
 
 @end
 
diff --git a/jre_emul/Classes/IOSProtocolClass.h b/jre_emul/Classes/IOSProtocolClass.h
index fba9a8e049..42e963d34d 100644
--- a/jre_emul/Classes/IOSProtocolClass.h
+++ b/jre_emul/Classes/IOSProtocolClass.h
@@ -24,7 +24,7 @@
 
 @interface IOSProtocolClass : IOSClass
 
-- (instancetype)initWithProtocol:(Protocol *)protocol;
+- (instancetype)initWithProtocol:(Protocol * _Nonnull)protocol;
 
 @end
 
diff --git a/jre_emul/Classes/J2ObjC_header.h b/jre_emul/Classes/J2ObjC_header.h
index 702a671366..5135ecacc3 100644
--- a/jre_emul/Classes/J2ObjC_header.h
+++ b/jre_emul/Classes/J2ObjC_header.h
@@ -15,6 +15,9 @@
 #ifndef _J2OBJC_HEADER_H_
 #define _J2OBJC_HEADER_H_
 
+#pragma clang diagnostic push
+#pragma GCC diagnostic ignored "-Wnullability-completeness"
+
 #import "IOSObjectArray.h"
 #import "J2ObjC_common.h"
 #import "JavaObject.h"
@@ -340,4 +343,6 @@ CF_EXTERN_C_END
 // can measure how much of the app's size is due to transpiled Java code.
 #define J2OBJC_TEXT_SEGMENT __attribute__((section("__TEXT,__j2objc_text")))
 
+#pragma clang diagnostic pop
+
 #endif  // _J2OBJC_HEADER_H_
diff --git a/jre_emul/Classes/JavaObject.h b/jre_emul/Classes/JavaObject.h
index 7b0c0a1a84..9a53eb90ed 100644
--- a/jre_emul/Classes/JavaObject.h
+++ b/jre_emul/Classes/JavaObject.h
@@ -30,10 +30,10 @@
 @protocol JavaObject <NSObject>
 
 // Returns a copy of the object, if it implements java.lang.Cloneable.
-- (id)java_clone;
+- (id _Nonnull)java_clone;
 
 // Returns the IOSClass of the receiver.
-- (IOSClass *)java_getClass;
+- (IOSClass * _Nonnull)java_getClass;
 
 // Wakes up a waiting thread (if any).
 - (void)java_notify;
diff --git a/jre_emul/Classes/JreEmulation.h b/jre_emul/Classes/JreEmulation.h
index 3866ce90d1..176aee472c 100644
--- a/jre_emul/Classes/JreEmulation.h
+++ b/jre_emul/Classes/JreEmulation.h
@@ -18,6 +18,9 @@
 #define _JreEmulation_H_
 
 #ifdef __OBJC__
+#pragma clang diagnostic push
+#pragma GCC diagnostic ignored "-Wnullability-completeness"
+
 #import "J2ObjC_common.h"
 #import "JavaObject.h"
 #import "IOSClass.h"
@@ -28,6 +31,8 @@
 #import "NSNumber+JavaNumber.h"
 #import "NSObject+JavaObject.h"
 #import "NSString+JavaString.h"
+
+#pragma clang diagnostic pop
 #endif // __OBJC__
 
 #endif // _JreEmulation_H_
diff --git a/jre_emul/Classes/NSDataInputStream.h b/jre_emul/Classes/NSDataInputStream.h
index 72d3c50767..857f487a71 100644
--- a/jre_emul/Classes/NSDataInputStream.h
+++ b/jre_emul/Classes/NSDataInputStream.h
@@ -15,11 +15,13 @@
 // a given NSData instance. The NSData instance is copied at
 // initialization, so further modifications (if it happened to
 // be mutable) will not be visible.
+NS_ASSUME_NONNULL_BEGIN
 @interface NSDataInputStream : JavaIoInputStream
 
 - (instancetype)initWithData:(NSData *)data;
 + (NSDataInputStream *)streamWithData:(NSData *)data;
 
 @end
+NS_ASSUME_NONNULL_END
 
 #endif // _NSDataInputStream_H_
diff --git a/jre_emul/Classes/NSDataOutputStream.h b/jre_emul/Classes/NSDataOutputStream.h
index ad62e705fd..54bd1947b1 100644
--- a/jre_emul/Classes/NSDataOutputStream.h
+++ b/jre_emul/Classes/NSDataOutputStream.h
@@ -13,6 +13,7 @@
 
 // A concrete subclass of java.io.InputStream that writes into
 // a backing NSData instance, retrievable at any point.
+NS_ASSUME_NONNULL_BEGIN
 @interface NSDataOutputStream : JavaIoOutputStream
 
 + (NSDataOutputStream *)stream;
@@ -23,5 +24,6 @@
 - (NSData *)data;
 
 @end
+NS_ASSUME_NONNULL_END
 
 #endif // _NSDataOutputStream_H_
diff --git a/jre_emul/Classes/NSDictionaryMap.h b/jre_emul/Classes/NSDictionaryMap.h
index 27665bd778..52b5cfcb44 100644
--- a/jre_emul/Classes/NSDictionaryMap.h
+++ b/jre_emul/Classes/NSDictionaryMap.h
@@ -18,6 +18,7 @@
 // The entrySet, keySet and valueSet methods return sets not backed
 // by the Map, so modifications to the map won't be reflected in the
 // sets and vice-versa.
+NS_ASSUME_NONNULL_BEGIN
 @interface NSDictionaryMap : JavaUtilAbstractMap < JavaUtilMap > {
  @private
   // The backing native map.
@@ -36,5 +37,6 @@
 - (void)forEachWithJavaUtilFunctionBiConsumer:(id<JavaUtilFunctionBiConsumer>)action;
 
 @end
+NS_ASSUME_NONNULL_END
 
 #endif // _NSDictionaryMap_H_
diff --git a/jre_emul/Classes/NSNumber+JavaNumber.h b/jre_emul/Classes/NSNumber+JavaNumber.h
index 97f7e21cbf..fe4d0e16aa 100644
--- a/jre_emul/Classes/NSNumber+JavaNumber.h
+++ b/jre_emul/Classes/NSNumber+JavaNumber.h
@@ -30,7 +30,7 @@
 
 @end
 
-__attribute__((always_inline)) inline void NSNumber_init(NSObject *self) {
+__attribute__((always_inline)) inline void NSNumber_init(NSObject * _Nonnull self) {
   #pragma unused(self)
 }
 
diff --git a/jre_emul/Classes/NSObject+JavaObject.h b/jre_emul/Classes/NSObject+JavaObject.h
index 865fbbfd6b..0408ada532 100644
--- a/jre_emul/Classes/NSObject+JavaObject.h
+++ b/jre_emul/Classes/NSObject+JavaObject.h
@@ -30,6 +30,7 @@
 @class IOSClass;
 
 // A category that adds Java Object-compatible methods to NSObject.
+NS_ASSUME_NONNULL_BEGIN
 @interface NSObject (JavaObject) <JavaObject>
 
 // JavaObject doesn't implement Comparable, but the Comparable contract wants
@@ -50,14 +51,16 @@
 - (void)_java_lang_ref_original_release;
 
 @end
+NS_ASSUME_NONNULL_END
 
-__attribute__((always_inline)) inline void NSObject_init(NSObject *self) {
-  #pragma unused(self)
+__attribute__((always_inline)) inline void NSObject_init(NSObject* _Nonnull self) {
+#pragma unused(self)
 }
-__attribute__((always_inline)) NS_RETURNS_RETAINED inline NSObject *new_NSObject_init(void) {
+__attribute__((always_inline)) NS_RETURNS_RETAINED inline NSObject* _Nonnull new_NSObject_init(
+    void) {
   return [NSObject alloc];
 }
-__attribute__((always_inline)) inline NSObject *create_NSObject_init(void) {
+__attribute__((always_inline)) inline NSObject* _Nonnull create_NSObject_init(void) {
   return AUTORELEASE([NSObject alloc]);
 }
 
diff --git a/jre_emul/Classes/NSString+JavaString.h b/jre_emul/Classes/NSString+JavaString.h
index 4bd5940e95..a02c72bbd1 100644
--- a/jre_emul/Classes/NSString+JavaString.h
+++ b/jre_emul/Classes/NSString+JavaString.h
@@ -19,7 +19,6 @@
 
 #if __has_feature(nullability)
 #pragma clang diagnostic push
-#pragma GCC diagnostic ignored "-Wnullability"
 #pragma GCC diagnostic ignored "-Wnullability-completeness"
 #endif
 
@@ -43,10 +42,11 @@
 // A category that adds java.lang.String-like methods to NSString.  The method
 // list is not exhaustive, since methods that can be directly substituted are
 // inlined.
+NS_ASSUME_NONNULL_BEGIN
 @interface NSString (JavaString) <JavaIoSerializable, JavaLangComparable, JavaLangCharSequence>
 
 // String.valueOf(Object)
-+ (nonnull NSString *)java_valueOf:(id<NSObject>)obj;
++ (nonnull NSString *)java_valueOf:(nullable id<NSObject>)obj;
 
 // String.valueOf(boolean)
 + (nonnull NSString *)java_valueOfBool:(jboolean)value;
@@ -222,7 +222,7 @@
 // String.format(String, ...), String.format(Locale, String, ...)
 + (nonnull NSString *)java_formatWithNSString:(NSString *)format
                             withNSObjectArray:(IOSObjectArray *)args;
-+ (nonnull NSString *)java_formatWithJavaUtilLocale:(JavaUtilLocale *)locale
++ (nonnull NSString *)java_formatWithJavaUtilLocale:(nullable JavaUtilLocale *)locale
                                        withNSString:(NSString *)format
                                   withNSObjectArray:(IOSObjectArray *)args;
 
@@ -305,6 +305,7 @@
 - (jboolean)java_isBlank;
 
 @end
+NS_ASSUME_NONNULL_END
 
 // String.format(Locale, String, Object...)
 FOUNDATION_EXPORT NSString *NSString_java_formatWithJavaUtilLocale_withNSString_withNSObjectArray_(
diff --git a/jre_emul/Classes/java/lang/AbstractStringBuilder.h b/jre_emul/Classes/java/lang/AbstractStringBuilder.h
index 8e4695dc2d..3c12fea90a 100644
--- a/jre_emul/Classes/java/lang/AbstractStringBuilder.h
+++ b/jre_emul/Classes/java/lang/AbstractStringBuilder.h
@@ -28,6 +28,7 @@ typedef struct JreStringBuilder {
   jint count_;
 } JreStringBuilder;
 
+NS_ASSUME_NONNULL_BEGIN
 @interface JavaLangAbstractStringBuilder : NSObject < JavaLangAppendable, JavaLangCharSequence > {
  @package
   JreStringBuilder delegate_;
@@ -141,4 +142,6 @@ NSString *JreStringBuilder_toStringAndDealloc(JreStringBuilder *sb);
 
 CF_EXTERN_C_END
 
+NS_ASSUME_NONNULL_END
+
 #endif // _JavaLangAbstractStringBuilder_H_