diff --git a/lldb/source/Plugins/Language/ObjC/Cocoa.cpp b/lldb/source/Plugins/Language/ObjC/Cocoa.cpp
--- a/lldb/source/Plugins/Language/ObjC/Cocoa.cpp
+++ b/lldb/source/Plugins/Language/ObjC/Cocoa.cpp
@@ -867,7 +867,7 @@
   // is generally true and POSIXly happy, but might break if a library vendor
   // decides to get creative
   time_t epoch = GetOSXEpoch();
-  epoch = epoch + (time_t)date_value;
+  epoch = epoch + static_cast<time_t>(std::floor(date_value));
   tm *tm_date = gmtime(&epoch);
   if (!tm_date)
     return false;
diff --git a/lldb/test/API/functionalities/data-formatter/data-formatter-objc/TestDataFormatterObjCNSDate.py b/lldb/test/API/functionalities/data-formatter/data-formatter-objc/TestDataFormatterObjCNSDate.py
--- a/lldb/test/API/functionalities/data-formatter/data-formatter-objc/TestDataFormatterObjCNSDate.py
+++ b/lldb/test/API/functionalities/data-formatter/data-formatter-objc/TestDataFormatterObjCNSDate.py
@@ -43,6 +43,15 @@
         self.expect('frame variable date4_abs', substrs=['1970'])
         self.expect('frame variable date5_abs', substrs=[now_year])
 
+        # Check that LLDB always follow's NSDate's rounding behavior (which
+        # is always rounding down).
+        self.expect_expr("date_1970_minus_06", result_summary="1969-12-31 23:59:59 UTC")
+        self.expect_expr("date_1970_minus_05", result_summary="1969-12-31 23:59:59 UTC")
+        self.expect_expr("date_1970_minus_04", result_summary="1969-12-31 23:59:59 UTC")
+        self.expect_expr("date_1970_plus_06", result_summary="1970-01-01 00:00:00 UTC")
+        self.expect_expr("date_1970_plus_05", result_summary="1970-01-01 00:00:00 UTC")
+        self.expect_expr("date_1970_plus_04", result_summary="1970-01-01 00:00:00 UTC")
+
         self.expect('frame variable cupertino home europe',
                     substrs=['@"America/Los_Angeles"',
                              '@"Europe/Rome"',
diff --git a/lldb/test/API/functionalities/data-formatter/data-formatter-objc/main.m b/lldb/test/API/functionalities/data-formatter/data-formatter-objc/main.m
--- a/lldb/test/API/functionalities/data-formatter/data-formatter-objc/main.m
+++ b/lldb/test/API/functionalities/data-formatter/data-formatter-objc/main.m
@@ -655,6 +655,14 @@
       [NSDate dateWithTimeIntervalSinceReferenceDate:
                   floor([[NSDate date] timeIntervalSinceReferenceDate])];
 
+  NSDate *date_1970_minus_06 = [NSDate dateWithTimeIntervalSince1970:-0.6];
+  NSDate *date_1970_minus_05 = [NSDate dateWithTimeIntervalSince1970:-0.5];
+  NSDate *date_1970_minus_04 = [NSDate dateWithTimeIntervalSince1970:-0.4];
+
+  NSDate *date_1970_plus_06 = [NSDate dateWithTimeIntervalSince1970:0.6];
+  NSDate *date_1970_plus_05 = [NSDate dateWithTimeIntervalSince1970:0.5];
+  NSDate *date_1970_plus_04 = [NSDate dateWithTimeIntervalSince1970:0.4];
+
   CFAbsoluteTime date1_abs = CFDateGetAbsoluteTime(date1);
   CFAbsoluteTime date2_abs = CFDateGetAbsoluteTime(date2);
   CFAbsoluteTime date3_abs = CFDateGetAbsoluteTime(date3);