diff --git a/Code/ObjectMapping/RKObjectMapping.h b/Code/ObjectMapping/RKObjectMapping.h
index c16b1509..babfab04 100644
--- a/Code/ObjectMapping/RKObjectMapping.h
+++ b/Code/ObjectMapping/RKObjectMapping.h
@@ -482,7 +482,7 @@ relationship. Relationships are processed using an object mapping as well.
 
 /**
  Convenience method for quickly constructing a date formatter and adding it to the collection of default
- date formatters
+ date formatters. The locale is auto-configured to en_US_POSIX
  
  @param dateFormatString The dateFormat string to assign to the newly constructed NSDateFormatter instance
  @param nilOrTimeZone The NSTimeZone object to configure on the NSDateFormatter instance. Defaults to UTC time.
diff --git a/Code/ObjectMapping/RKObjectMapping.m b/Code/ObjectMapping/RKObjectMapping.m
index eba06638..825c48f2 100644
--- a/Code/ObjectMapping/RKObjectMapping.m
+++ b/Code/ObjectMapping/RKObjectMapping.m
@@ -322,6 +322,7 @@ static NSDateFormatter *preferredDateFormatter = nil;
 + (void)addDefaultDateFormatterForString:(NSString *)dateFormatString inTimeZone:(NSTimeZone *)nilOrTimeZone {
     NSDateFormatter *dateFormatter = [NSDateFormatter new];
     dateFormatter.dateFormat = dateFormatString;
+    dateFormatter.locale = [[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"] autorelease];
     if (nilOrTimeZone) {
         dateFormatter.timeZone = nilOrTimeZone;
     } else {
@@ -337,6 +338,7 @@ static NSDateFormatter *preferredDateFormatter = nil;
         preferredDateFormatter = [NSDateFormatter new];
         [preferredDateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss Z"];
         preferredDateFormatter.timeZone = [NSTimeZone timeZoneWithAbbreviation:@"UTC"];
+        preferredDateFormatter.locale = [[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"] autorelease];
     }
     
     return preferredDateFormatter;