diff --git a/.changesets/check-argument-type-of-breadcrumb-metadata.md b/.changesets/check-argument-type-of-breadcrumb-metadata.md
new file mode 100644
index 000000000..501d32b61
--- /dev/null
+++ b/.changesets/check-argument-type-of-breadcrumb-metadata.md
@@ -0,0 +1,15 @@
+---
+bump: "patch"
+type: "fix"
+---
+
+Log error when the argument type of the breadcrumb metadata is invalid. This metadata argument should be a Hash, and other values are not supported. More information can be found in the [Ruby gem breadcrumb documentation](https://docs.appsignal.com/ruby/instrumentation/breadcrumbs.html).
+
+```ruby
+Appsignal.add_breadcrumb(
+  "breadcrumb category",
+  "breadcrumb action",
+  "some message",
+  { :metadata_key => "some value" } # This needs to be a Hash object
+)
+```
diff --git a/lib/appsignal/transaction.rb b/lib/appsignal/transaction.rb
index 402f97648..ff69bf239 100644
--- a/lib/appsignal/transaction.rb
+++ b/lib/appsignal/transaction.rb
@@ -186,6 +186,12 @@ def set_tags(given_tags = {})
     # @see https://docs.appsignal.com/ruby/instrumentation/breadcrumbs.html
     #   Breadcrumb reference
     def add_breadcrumb(category, action, message = "", metadata = {}, time = Time.now.utc)
+      unless metadata.is_a? Hash
+        Appsignal.logger.error "add_breadcrumb: Cannot add breadcrumb. " \
+          "The given metadata argument is not a Hash."
+        return
+      end
+
       @breadcrumbs.push(
         :time => time.to_i,
         :category => category,
diff --git a/spec/lib/appsignal/transaction_spec.rb b/spec/lib/appsignal/transaction_spec.rb
index c825be0f7..c25cd50ee 100644
--- a/spec/lib/appsignal/transaction_spec.rb
+++ b/spec/lib/appsignal/transaction_spec.rb
@@ -432,6 +432,19 @@ def current_transaction
           expect(breadcrumb["metadata"]).to eq({})
         end
       end
+
+      context "with metadata argument that's not a Hash" do
+        it "does not add the breadcrumb and logs and error" do
+          transaction.add_breadcrumb("category", "action", "message", "invalid metadata")
+          transaction.sample_data
+
+          expect(transaction.to_h["sample_data"]["breadcrumbs"]).to be_empty
+          expect(log_contents(log)).to contains_log(
+            :error,
+            "add_breadcrumb: Cannot add breadcrumb. The given metadata argument is not a Hash."
+          )
+        end
+      end
     end
 
     describe "#set_action" do