diff --git a/src/calibre/ebooks/metadata/book/base.py b/src/calibre/ebooks/metadata/book/base.py
index 4eafdab282..b8f85dc05b 100644
--- a/src/calibre/ebooks/metadata/book/base.py
+++ b/src/calibre/ebooks/metadata/book/base.py
@@ -822,8 +822,12 @@ def field_from_string(field, raw, field_metadata):
     elif dt == 'rating':
         val = float(raw) * 2
     elif dt == 'datetime':
-        from calibre.utils.date import parse_only_date
-        val = parse_only_date(raw)
+        from calibre.utils.iso8601 import parse_iso8601
+        try:
+            val = parse_iso8601(raw, require_aware=True)
+        except Exception:
+            from calibre.utils.date import parse_only_date
+            val = parse_only_date(raw)
     elif dt == 'bool':
         if raw.lower() in {'true', 'yes', 'y'}:
             val = True
diff --git a/src/calibre/utils/iso8601.py b/src/calibre/utils/iso8601.py
index eb4ffeca95..fc8ef91c93 100644
--- a/src/calibre/utils/iso8601.py
+++ b/src/calibre/utils/iso8601.py
@@ -42,7 +42,7 @@ del tzutc, tzlocal
 UNDEFINED_DATE = datetime(101,1,1, tzinfo=utc_tz)
 
 
-def parse_iso8601(date_string, assume_utc=False, as_utc=True):
+def parse_iso8601(date_string, assume_utc=False, as_utc=True, require_aware=False):
     if not date_string:
         return UNDEFINED_DATE
     dt, aware, tzseconds = speedup.parse_iso8601(date_string)
@@ -54,6 +54,8 @@ def parse_iso8601(date_string, assume_utc=False, as_utc=True):
             sign = '-' if tzseconds < 0 else '+'
             description = "%s%02d:%02d" % (sign, abs(tzseconds) // 3600, (abs(tzseconds) % 3600) // 60)
             tz = tzoffset(description, tzseconds)
+    elif require_aware:
+        raise ValueError('{} does not specify a time zone'.format(date_string))
     dt = dt.replace(tzinfo=tz)
     if as_utc and tz is utc_tz:
         return dt