diff --git a/changelog/fix_fix_railscompactblank_bug_when_offense.md b/changelog/fix_fix_railscompactblank_bug_when_offense.md
new file mode 100644
index 0000000000..057e02e152
--- /dev/null
+++ b/changelog/fix_fix_railscompactblank_bug_when_offense.md
@@ -0,0 +1 @@
+* [#753](https://github.com/rubocop/rubocop-rails/pull/753): Fix `Rails/CompactBlank` bug when offense is found in block. ([@r7kamura][])
diff --git a/lib/rubocop/cop/rails/compact_blank.rb b/lib/rubocop/cop/rails/compact_blank.rb
index 8efcf30f1d..fe5e88448f 100644
--- a/lib/rubocop/cop/rails/compact_blank.rb
+++ b/lib/rubocop/cop/rails/compact_blank.rb
@@ -93,7 +93,11 @@ def use_hash_value_block_argument?(arguments, receiver_in_block)
         end
 
         def offense_range(node)
-          end_pos = node.parent&.block_type? ? node.parent.loc.expression.end_pos : node.loc.expression.end_pos
+          end_pos = if node.parent&.block_type? && node.parent&.send_node == node
+                      node.parent.loc.expression.end_pos
+                    else
+                      node.loc.expression.end_pos
+                    end
 
           range_between(node.loc.selector.begin_pos, end_pos)
         end
diff --git a/spec/rubocop/cop/rails/compact_blank_spec.rb b/spec/rubocop/cop/rails/compact_blank_spec.rb
index 059bf81d5a..a1f459c892 100644
--- a/spec/rubocop/cop/rails/compact_blank_spec.rb
+++ b/spec/rubocop/cop/rails/compact_blank_spec.rb
@@ -68,6 +68,17 @@
       RUBY
     end
 
+    it 'registers and corrects an offense when using `reject(&:blank?)` in block' do
+      expect_offense(<<~RUBY)
+        hash.transform_values { |value| value.reject(&:blank?) }
+                                              ^^^^^^^^^^^^^^^^ Use `compact_blank` instead.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        hash.transform_values { |value| value.compact_blank }
+      RUBY
+    end
+
     it 'does not register an offense when using `compact_blank`' do
       expect_no_offenses(<<~RUBY)
         collection.compact_blank