diff --git a/Code/Support/RKMIMETypeSerialization.m b/Code/Support/RKMIMETypeSerialization.m
index fc2cf90b..2680f210 100644
--- a/Code/Support/RKMIMETypeSerialization.m
+++ b/Code/Support/RKMIMETypeSerialization.m
@@ -146,6 +146,9 @@
 
 + (id)objectFromData:(NSData *)data MIMEType:(NSString *)MIMEType error:(NSError **)error
 {
+    NSParameterAssert(data);
+    NSParameterAssert(MIMEType);
+
     Class<RKSerialization> serializationClass = [self serializationClassForMIMEType:MIMEType];
     if (!serializationClass) {
         if (error) {
@@ -161,6 +164,8 @@
 
 + (id)dataFromObject:(id)object MIMEType:(NSString *)MIMEType error:(NSError **)error
 {
+    NSParameterAssert(object);
+    NSParameterAssert(MIMEType);
     Class<RKSerialization> serializationClass = [self serializationClassForMIMEType:MIMEType];
     if (!serializationClass) {
         if (error) {
diff --git a/Code/Testing/RKTestFixture.m b/Code/Testing/RKTestFixture.m
index 702a858f..920fd6c6 100644
--- a/Code/Testing/RKTestFixture.m
+++ b/Code/Testing/RKTestFixture.m
@@ -86,14 +86,12 @@ static NSBundle *fixtureBundle = nil;
 {
     NSError *error = nil;
     NSData *resourceContents = [self dataWithContentsOfFixture:fixtureName];
+    NSAssert(resourceContents, @"Failed to read fixture named '%@'", fixtureName);
     NSString *MIMEType = [self MIMETypeForFixture:fixtureName];
+    NSAssert(MIMEType, @"Failed to determine MIME type of fixture named '%@'", fixtureName);
     
     id object = [RKMIMETypeSerialization objectFromData:resourceContents MIMEType:MIMEType error:&error];
-    if (object == nil) {
-        RKLogCritical(@"Failed to parse fixture name '%@' in bundle %@. Error: %@", fixtureName, [self fixtureBundle], [error localizedDescription]);
-        return nil;
-    }
-    
+    NSAssert(object, @"Failed to parse fixture name '%@' in bundle %@. Error: %@", fixtureName, [self fixtureBundle], [error localizedDescription]);
     return object;
 }