diff --git a/src/cligen/flag.cr b/src/cligen/flag.cr
index c301de2..45ddde7 100644
--- a/src/cligen/flag.cr
+++ b/src/cligen/flag.cr
@@ -248,16 +248,39 @@ module CliGen
       {% elsif T == Time %}
         parse_time(raw)
       {% elsif T <= Array %}
-        {% elem = T.type_vars.first %}
-        {% if elem == Int32 %}
-          raw.split(@delimiter).map(&.to_i)
-        {% elsif elem == String %}
-          raw.split(@delimiter)
-        {% elsif elem.class < CliGen::Coercable %}
-          raw.split(@delimiter).map{|i| {{elem}}.coerce(i)}
-        {% else %}
-          {% raise "ERROR : Flag(#{T}) : #{elem} is not a coercable type. If you wish to coerce it from a bare string extend CliGen::Coercable & implement the class method" %}
-        {% end %}
+        if raw.includes?(@delimiter)
+          {% elem = T.type_vars.first %}
+          raw.split(@delimiter).map do |val|
+            unless @format.nil?
+              abort "ERROR : Flag({{T}}, long: #{@long_key}) : #{val} does not match a valid format" unless val =~ @format
+            end
+
+            {% if elem == Int32 %}
+              abort "ERROR : Flag({{T}}, long: #{@long_key}) : #{val} is not an integer" unless val =~ /^[[:digit:]]+$/
+              val.to_i
+            {% elsif elem == String %}
+              val
+            {% elsif elem.class < CliGen::Coercable %}
+              {{elem}}.coerce(val)
+            {% else %}
+              {% raise "ERROR : Flag(#{T}) : #{elem} is not a coercable type. If you wish to coerce it from a bare string extend CliGen::Coercable & implement the class method" %}
+            {% end %}
+          end
+        else
+          unless @format.nil?
+            abort "ERROR : Flag({{T}}, long: #{@long_key}) : #{raw} does not match a valid format" unless raw =~ @format
+          end
+          {% if elem == Int32 %}
+            abort "ERROR : Flag({{T}}, long: #{@long_key}) : #{raw} is not an integer" unless raw =~ /^[[:digit:]]+$/
+            [ raw.to_i ]
+          {% elsif elem == String %}
+            [ raw ]
+          {% elsif elem.class < CliGen::Coercable %}
+            [ {{elem}}.coerce(raw) ]
+          {% else %}
+            {% raise "ERROR : Flag(#{T}) : #{T} is not a coercable type. If you wish to coerce it from a bare string extend CliGen::Coercable & implement the class method" %}
+          {% end %}
+        end
       {% elsif T == String %} # String
         raw
       {% elsif T.class < CliGen::Coercable %}