diff --git a/spec/std/time/time_spec.cr b/spec/std/time/time_spec.cr
index 7b55eb5776aa..e8bdfe1de3fb 100644
--- a/spec/std/time/time_spec.cr
+++ b/spec/std/time/time_spec.cr
@@ -624,6 +624,15 @@ describe Time do
     time.location.fixed?.should be_true
   end
 
+  it "raises when time zone missing" do
+    expect_raises(Time::Format::Error, "Invalid timezone") do
+      Time.parse("", "%z")
+    end
+    expect_raises(Time::Format::Error, "Invalid timezone") do
+      Time.parse("123456+01:00", "%3N%z")
+    end
+  end
+
   # TODO %Z
   # TODO %G
   # TODO %g
diff --git a/src/http/common.cr b/src/http/common.cr
index b94e4a7a987b..604e06e76b72 100644
--- a/src/http/common.cr
+++ b/src/http/common.cr
@@ -4,7 +4,8 @@
 {% end %}
 
 module HTTP
-  private DATE_PATTERNS = {"%a, %d %b %Y %H:%M:%S %z", "%d %b %Y %H:%M:%S %z", "%A, %d-%b-%y %H:%M:%S %z", "%a %b %e %H:%M:%S %Y"}
+  private DATE_PATTERNS = {"%a, %d %b %Y %H:%M:%S %z", "%d %b %Y %H:%M:%S %z", "%A, %d-%b-%y %H:%M:%S %z", "%a %b %e %H:%M:%S %Y",
+                           "%a, %d %b %Y %H:%M:%S GMT", "%d %b %Y %H:%M:%S GMT", "%A, %d-%b-%y %H:%M:%S GMT", "%a %b %e %H:%M:%S %Y"}
 
   # :nodoc:
   MAX_HEADER_SIZE = 16_384
diff --git a/src/time/format/parser.cr b/src/time/format/parser.cr
index 6b23fd1a60e4..faca5bf4f45b 100644
--- a/src/time/format/parser.cr
+++ b/src/time/format/parser.cr
@@ -284,6 +284,8 @@ struct Time::Format
             @reader.pos = pos
           end
         end
+      else
+        raise "Invalid timezone"
       end
     end