diff --git a/Code/ObjectMapping/RKObjectMapping.m b/Code/ObjectMapping/RKObjectMapping.m
index 6003dbbe..2a569eb5 100644
--- a/Code/ObjectMapping/RKObjectMapping.m
+++ b/Code/ObjectMapping/RKObjectMapping.m
@@ -157,6 +157,7 @@ NSDate *RKDateFromStringWithFormatters(NSString *dateString, NSArray *formatters
 
 - (void)addPropertyMappingsFromArray:(NSArray *)arrayOfPropertyMappings
 {
+    NSAssert([[arrayOfPropertyMappings valueForKeyPath:@"@distinctUnionOfObjects.objectMapping"] count] == 0, @"One or more of the property mappings in the given array has already been added to another `RKObjectMapping` object. You probably want to obtain a copy of the array of mappings: `[[NSArray alloc] initWithArray:arrayOfPropertyMappings copyItems:YES]`");
     for (RKPropertyMapping *propertyMapping in arrayOfPropertyMappings) {
         [self addPropertyMapping:propertyMapping];
     }
@@ -204,16 +205,19 @@ NSDate *RKDateFromStringWithFormatters(NSString *dateString, NSArray *formatters
 
 - (void)addAttributeMappingsFromArray:(NSArray *)arrayOfAttributeNamesOrMappings
 {
+    NSMutableArray *arrayOfAttributeMappings = [NSMutableArray arrayWithCapacity:[arrayOfAttributeNamesOrMappings count]];
     for (id entry in arrayOfAttributeNamesOrMappings) {
         if ([entry isKindOfClass:[NSString class]]) {
-            [self addPropertyMapping:[RKAttributeMapping attributeMappingFromKeyPath:entry toKeyPath:entry]];
+            [arrayOfAttributeMappings addObject:[RKAttributeMapping attributeMappingFromKeyPath:entry toKeyPath:entry]];
         } else if ([entry isKindOfClass:[RKAttributeMapping class]]) {
-            [self addPropertyMapping:entry];
+            [arrayOfAttributeMappings addObject:entry];
         } else {
             [NSException raise:NSInvalidArgumentException
                         format:@"*** - [%@ %@]: Unable to attribute mapping from unsupported entry of type '%@' (%@).", NSStringFromClass([self class]), NSStringFromSelector(_cmd), NSStringFromClass([entry class]), entry];
         }
     }
+
+    [self addPropertyMappingsFromArray:arrayOfAttributeMappings];
 }
 
 - (void)removePropertyMapping:(RKPropertyMapping *)attributeOrRelationshipMapping
diff --git a/Tests/Logic/ObjectMapping/RKObjectMappingTest.m b/Tests/Logic/ObjectMapping/RKObjectMappingTest.m
index 61efb06c..a2e65a42 100644
--- a/Tests/Logic/ObjectMapping/RKObjectMappingTest.m
+++ b/Tests/Logic/ObjectMapping/RKObjectMappingTest.m
@@ -105,4 +105,64 @@
     assertThatBool([mapping1 isEqualToMapping:mapping2], is(equalToBool(NO)));
 }
 
+- (void)testThatAddingAPropertyMappingThatExistsInAnotherMappingTriggersException
+{
+    RKObjectMapping *firstMapping = [RKObjectMapping mappingForClass:[NSMutableDictionary class]];
+    RKAttributeMapping *attributeMapping = [RKAttributeMapping attributeMappingFromKeyPath:@"this" toKeyPath:@"that"];
+    [firstMapping addPropertyMapping:attributeMapping];
+
+    RKObjectMapping *secondMapping = [RKObjectMapping mappingForClass:[NSMutableDictionary class]];
+    NSException *exception = nil;
+    @try {
+        [secondMapping addPropertyMapping:attributeMapping];
+    }
+    @catch (NSException *caughtException) {
+        exception = caughtException;
+    }
+    @finally {
+        expect(exception).notTo.beNil();
+        expect(exception.reason).to.equal(@"Cannot add a property mapping object that has already been added to another `RKObjectMapping` object. You probably want to obtain a copy of the mapping: `[propertyMapping copy]`");
+    }
+}
+
+- (void)testThatAddingAnArrayOfPropertyMappingsThatExistInAnotherMappingTriggersException
+{
+    RKObjectMapping *firstMapping = [RKObjectMapping mappingForClass:[NSMutableDictionary class]];
+    RKAttributeMapping *attributeMapping = [RKAttributeMapping attributeMappingFromKeyPath:@"this" toKeyPath:@"that"];
+    [firstMapping addPropertyMapping:attributeMapping];
+
+    RKObjectMapping *secondMapping = [RKObjectMapping mappingForClass:[NSMutableDictionary class]];
+    NSException *exception = nil;
+    @try {
+        [secondMapping addPropertyMappingsFromArray:@[attributeMapping]];
+    }
+    @catch (NSException *caughtException) {
+        exception = caughtException;
+    }
+    @finally {
+        expect(exception).notTo.beNil();
+        expect(exception.reason).to.equal(@"One or more of the property mappings in the given array has already been added to another `RKObjectMapping` object. You probably want to obtain a copy of the array of mappings: `[[NSArray alloc] initWithArray:arrayOfPropertyMappings copyItems:YES]`");
+    }
+}
+
+- (void)testThatAddingAnArrayOfAttributeMappingsThatExistInAnotherMappingTriggersException
+{
+    RKObjectMapping *firstMapping = [RKObjectMapping mappingForClass:[NSMutableDictionary class]];
+    RKAttributeMapping *attributeMapping = [RKAttributeMapping attributeMappingFromKeyPath:@"this" toKeyPath:@"that"];
+    [firstMapping addPropertyMapping:attributeMapping];
+
+    RKObjectMapping *secondMapping = [RKObjectMapping mappingForClass:[NSMutableDictionary class]];
+    NSException *exception = nil;
+    @try {
+        [secondMapping addAttributeMappingsFromArray:@[attributeMapping, @"stringValue"]];
+    }
+    @catch (NSException *caughtException) {
+        exception = caughtException;
+    }
+    @finally {
+        expect(exception).notTo.beNil();
+        expect(exception.reason).to.equal(@"One or more of the property mappings in the given array has already been added to another `RKObjectMapping` object. You probably want to obtain a copy of the array of mappings: `[[NSArray alloc] initWithArray:arrayOfPropertyMappings copyItems:YES]`");
+    }
+}
+
 @end