diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7804197..3f37216 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
 * Replace `minitest` gem with `rspec`
 * Fancier README
 * Remove unnecessary short circuit in `randomize` method
+* Add ability for `:on` argument to accept a `Hash` where the keys are exception types and the values are either `Proc`s or arrays of `Proc`s that will evaluate to `true` when the exception should be retried.
 
 ## 3.1.1
 
diff --git a/README.md b/README.md
index 551b14c..880498b 100644
--- a/README.md
+++ b/README.md
@@ -97,8 +97,9 @@ Here are the available options, in some vague order of relevance to most common
 - An `Array` of `Exception` classes (retry any exception of one of these types, including subclasses)
 - A `Hash` where the keys are `Exception` classes and the values are one of:
   - `nil` (retry every exception of the key's type, including subclasses)
+  - A single `Proc` (retries exceptions ONLY if it returns truthy)
   - A single `Regexp` pattern (retries exceptions ONLY if their `message` matches the pattern)
-  - An array of patterns (retries exceptions ONLY if their `message` matches at least one of the patterns)
+  - An array of `Proc` and/or `Regexp` (retries exceptions ONLY if at least one exception message matches a `Regexp` or at least one `Proc` returns `truthy`)
 
 
 ### Configuration
@@ -132,10 +133,15 @@ end
 
 You can also use a hash to specify that you only want to retry exceptions with certain messages (see [the documentation above](#configuring-which-options-to-retry-with-on)).  This example will retry all `ActiveRecord::RecordNotUnique` exceptions, `ActiveRecord::RecordInvalid` exceptions where the message matches either `/Parent must exist/` or `/Username has already been taken/`, or `Mysql2::Error` exceptions where the message matches `/Duplicate entry/`.
 
+A `Regexp` (or array of `Regexp`s). If any of the `Regexp`s match the exception's message, the block will be retried.
+A `Proc` (or array of `Proc`s) that evaluates the exception being handled and returns `true` if the block should be retried. If any of the procs in the list return `true`, the block will be retried.
+You can also mix and match `Proc`s and `Regexp`s in an `Array`
+
 ```ruby
 Retriable.retriable(on: {
   ActiveRecord::RecordNotUnique => nil,
   ActiveRecord::RecordInvalid => [/Parent must exist/, /Username has already been taken/],
+  ActiveRecord::RecordNotFound => -> (exception, try, elapsed_time, next_interval) { exception.model == User }
   Mysql2::Error => /Duplicate entry/
 }) do
   # code here...
diff --git a/lib/retriable.rb b/lib/retriable.rb
index c944093..a80adc1 100644
--- a/lib/retriable.rb
+++ b/lib/retriable.rb
@@ -60,17 +60,33 @@ def retriable(opts = {})
         return Timeout.timeout(timeout) { return yield(try) } if timeout
         return yield(try)
       rescue *[*exception_list] => exception
-        if on.is_a?(Hash)
-          raise unless exception_list.any? do |e|
-            exception.is_a?(e) && ([*on[e]].empty? || [*on[e]].any? { |pattern| exception.message =~ pattern })
-          end
-        end
-
         interval = intervals[index]
+        raise unless matched_exception?(on, exception, try, elapsed_time.call, interval)
+
         on_retry.call(exception, try, elapsed_time.call, interval) if on_retry
         raise if try >= tries || (elapsed_time.call + interval) > max_elapsed_time
         sleep interval if sleep_disabled != true
       end
     end
   end
+
+  def matched_exception?(on, exception, *proc_args)
+    return true unless on.is_a?(Hash)
+
+    on.any? do |expected_exception, matchers|
+      next false unless exception.is_a?(expected_exception)
+      next true if matchers.nil?
+
+      Array(matchers).any? do |matcher|
+        if matcher.is_a?(Regexp)
+          exception.message =~ matcher
+        elsif matcher.is_a?(Proc)
+          matcher.call(exception, *proc_args)
+        else
+          raise ArgumentError, "Exception hash values must be Proc or Regexp"
+        end
+      end
+    end
+  end
+  private_class_method :matched_exception?
 end
diff --git a/spec/retriable_spec.rb b/spec/retriable_spec.rb
index 5084e2f..f438eff 100644
--- a/spec/retriable_spec.rb
+++ b/spec/retriable_spec.rb
@@ -207,6 +207,34 @@ def increment_tries_with_exception(exception_class = nil)
       end
     end
 
+    it "#retriable retries with a hash exception where the value is a proc that returns true" do
+      matcher = lambda do |e, _try, _elapsed_time, _next_interval|
+        e.message == "something went wrong"
+      end
+      tries = 0
+      expect {
+        subject.retriable on: { NonStandardError => matcher }, tries: 2 do
+          tries += 1
+          raise NonStandardError, "something went wrong"
+        end
+      }.to raise_error NonStandardError
+
+      expect(tries).to eq 2
+    end
+
+    it "#retriable does not retry with a hash exception where the value is a proc that returns false" do
+      matcher = ->(e, *_args) { e.message == "something went wrong" }
+      tries = 0
+      expect {
+        subject.retriable on: { NonStandardError => matcher }, tries: 2 do
+          tries += 1
+          raise NonStandardError, "not a match"
+        end
+      }.to raise_error NonStandardError
+
+      expect(tries).to eq 1
+    end
+
     it "runs for a max elapsed time of 2 seconds" do
       described_class.configure { |c| c.sleep_disabled = false }