diff --git a/spec/ameba/rule/performance/join_after_map_spec.cr b/spec/ameba/rule/performance/map_instead_of_block_spec.cr
similarity index 87%
rename from spec/ameba/rule/performance/join_after_map_spec.cr
rename to spec/ameba/rule/performance/map_instead_of_block_spec.cr
index 46f5d250..6a8c468a 100644
--- a/spec/ameba/rule/performance/join_after_map_spec.cr
+++ b/spec/ameba/rule/performance/map_instead_of_block_spec.cr
@@ -1,13 +1,14 @@
 require "../../../spec_helper"
 
 module Ameba::Rule::Performance
-  subject = JoinAfterMap.new
+  subject = MapInsteadOfBlock.new
 
-  describe JoinAfterMap do
+  describe MapInsteadOfBlock do
     it "passes if there is no potential performance improvements" do
       source = Source.new %(
         (1..3).join(&.to_s)
-        (1..3).join('.', &.to_s)
+        (1..3).sum(&.*(2))
+        (1..3).product(&.*(2))
       )
       subject.catch(source).should be_valid
     end
@@ -52,7 +53,7 @@ module Ameba::Rule::Performance
       issue.rule.should_not be_nil
       issue.location.to_s.should eq "source.cr:1:8"
       issue.end_location.to_s.should eq "source.cr:1:24"
-      issue.message.should eq "Use `join(separator) {...}` instead of `map {...}.join(separator)`"
+      issue.message.should eq "Use `join {...}` instead of `map {...}.join`"
     end
   end
 end
diff --git a/src/ameba/rule/performance/join_after_map.cr b/src/ameba/rule/performance/map_instead_of_block.cr
similarity index 54%
rename from src/ameba/rule/performance/join_after_map.cr
rename to src/ameba/rule/performance/map_instead_of_block.cr
index 3cd74263..334eda2f 100644
--- a/src/ameba/rule/performance/join_after_map.cr
+++ b/src/ameba/rule/performance/map_instead_of_block.cr
@@ -1,32 +1,35 @@
 module Ameba::Rule::Performance
-  # This rule is used to identify usage of `join` calls that follow `map`.
+  # This rule is used to identify usage of `join/sum/product` calls
+  # that follow `map`.
   #
   # For example, this is considered inefficient:
   #
   # ```
   # (1..3).map(&.to_s).join('.')
+  # (1..3).map(&.*(2)).sum
   # ```
   #
   # And can be written as this:
   #
   # ```
   # (1..3).join('.', &.to_s)
+  # (1..3).sum(&.*(2))
   # ```
   #
   # YAML configuration example:
   #
   # ```
-  # Performance/JoinAfterMap
+  # Performance/MapInsteadOfBlock
   #   Enabled: true
   # ```
-  struct JoinAfterMap < Base
+  struct MapInsteadOfBlock < Base
     properties do
-      description "Identifies usage of `join` calls that follow `map`."
+      description "Identifies usage of `join/sum/product` calls that follow `map`."
     end
 
-    MAP_NAME  = "map"
-    JOIN_NAME = "join"
-    MSG       = "Use `join(separator) {...}` instead of `map {...}.join(separator)`"
+    CALL_NAMES = %w(join sum product)
+    MAP_NAME   = "map"
+    MSG        = "Use `%s {...}` instead of `map {...}.%s`"
 
     def test(source)
       AST::NodeVisitor.new self, source, skip: [
@@ -38,11 +41,12 @@ module Ameba::Rule::Performance
     end
 
     def test(source, node : Crystal::Call)
-      return unless node.name == JOIN_NAME && (obj = node.obj)
+      return unless node.name.in?(CALL_NAMES) && (obj = node.obj)
       return unless obj.is_a?(Crystal::Call) && obj.block
       return unless obj.name == MAP_NAME
 
-      issue_for obj.name_location, node.name_end_location, MSG
+      issue_for obj.name_location, node.name_end_location,
+        MSG % {node.name, node.name}
     end
   end
 end