diff --git a/ruby/lib/asciidoctor/extensions/asciidoctor_kroki/extension.rb b/ruby/lib/asciidoctor/extensions/asciidoctor_kroki/extension.rb
index d25049c0..6213283c 100644
--- a/ruby/lib/asciidoctor/extensions/asciidoctor_kroki/extension.rb
+++ b/ruby/lib/asciidoctor/extensions/asciidoctor_kroki/extension.rb
@@ -208,13 +208,13 @@ def get_role(format, role)
       end
 
       def get_format(doc, attrs, diagram_type)
-        format = attrs['format'] || 'svg'
-        # The JavaFX preview doesn't support SVG well, therefore we'll use PNG format...
-        if doc.attr?('env-idea') && format == 'svg'
-          # ... unless the diagram library does not support PNG as output format!
+        format = attrs['format'] || doc.attr('kroki-default-format') || 'svg'
+        if format == 'png'
+          # redirect PNG format to SVG if the diagram library only supports SVG as output format.
+          # this is useful when the default format has been set to PNG
           # Currently, mermaid, nomnoml, svgbob, wavedrom only support SVG as output format.
-          svg_only_diagram_types = %w[:mermaid :nomnoml :svgbob :wavedrom]
-          format = 'png' unless svg_only_diagram_types.include?(diagram_type)
+          svg_only_diagram_types = %i[mermaid nomnoml svgbob wavedrom]
+          format = 'svg' if svg_only_diagram_types.include?(diagram_type)
         end
         format
       end
diff --git a/ruby/spec/asciidoctor_kroki_spec.rb b/ruby/spec/asciidoctor_kroki_spec.rb
index 37a6137b..70fdf840 100644
--- a/ruby/spec/asciidoctor_kroki_spec.rb
+++ b/ruby/spec/asciidoctor_kroki_spec.rb
@@ -20,18 +20,33 @@
 </div>
 </div>)
     end
-    it 'should use png if env-idea is defined' do
+    it 'should use png if kroki-default-format is set to png' do
       input = <<~'ADOC'
         [plantuml]
         ....
         alice -> bob: hello
         ....
       ADOC
-      output = Asciidoctor.convert(input, attributes: { 'env-idea' => '' }, standalone: false)
+      output = Asciidoctor.convert(input, attributes: { 'kroki-default-format' => 'png' }, standalone: false)
       (expect output).to eql %(<div class="imageblock kroki">
 <div class="content">
 <img src="https://kroki.io/plantuml/png/eNpLzMlMTlXQtVNIyk-yUshIzcnJBwA9iwZL" alt="Diagram">
 </div>
+</div>)
+    end
+    it 'should use svg if kroki-default-format is set to png and the diagram type does not support png' do
+      input = <<~'ADOC'
+        [mermaid]
+        ....
+        graph TD;
+          A-->B;
+        ....
+      ADOC
+      output = Asciidoctor.convert(input, attributes: { 'kroki-default-format' => 'png' }, standalone: false)
+      (expect output).to eql %(<div class="imageblock kroki">
+<div class="content">
+<img src="https://kroki.io/mermaid/svg/eNpLL0osyFAIcbHmUlBw1NW1c7IGADLKBKY=" alt="Diagram">
+</div>
 </div>)
     end
     it 'should include the plantuml-include file when safe mode is safe' do
@@ -41,10 +56,12 @@
         alice -> bob: hello
         ....
       ADOC
-      output = Asciidoctor.convert(input, attributes: { 'env-idea' => '', 'kroki-plantuml-include' => 'spec/fixtures/config.puml' }, standalone: false, safe: :safe)
+      output = Asciidoctor.convert(input,
+                                   attributes: { 'kroki-plantuml-include' => 'spec/fixtures/config.puml' },
+                                   standalone: false, safe: :safe)
       (expect output).to eql %(<div class="imageblock kroki">
 <div class="content">
-<img src="https://kroki.io/plantuml/png/eNorzs7MK0gsSsxVyM3Py0_OKMrPTVUoKSpN5eJKzMlMTlXQtVNIyk-yUshIzcnJBwCT9xBc" alt="Diagram">
+<img src="https://kroki.io/plantuml/svg/eNorzs7MK0gsSsxVyM3Py0_OKMrPTVUoKSpN5eJKzMlMTlXQtVNIyk-yUshIzcnJBwCT9xBc" alt="Diagram">
 </div>
 </div>)
     end
@@ -55,10 +72,10 @@
         alice -> bob: hello
         ....
       ADOC
-      output = Asciidoctor.convert(input, attributes: { 'env-idea' => '', 'kroki-plantuml-include' => '../../../spec/fixtures/config.puml' }, standalone: false, safe: :safe)
+      output = Asciidoctor.convert(input, attributes: { 'kroki-plantuml-include' => '../../../spec/fixtures/config.puml' }, standalone: false, safe: :safe)
       (expect output).to eql %(<div class="imageblock kroki">
 <div class="content">
-<img src="https://kroki.io/plantuml/png/eNorzs7MK0gsSsxVyM3Py0_OKMrPTVUoKSpN5eJKzMlMTlXQtVNIyk-yUshIzcnJBwCT9xBc" alt="Diagram">
+<img src="https://kroki.io/plantuml/svg/eNorzs7MK0gsSsxVyM3Py0_OKMrPTVUoKSpN5eJKzMlMTlXQtVNIyk-yUshIzcnJBwCT9xBc" alt="Diagram">
 </div>
 </div>)
     end
@@ -69,10 +86,10 @@
         alice -> bob: hello
         ....
       ADOC
-      output = Asciidoctor.convert(input, attributes: { 'env-idea' => '', 'kroki-plantuml-include' => '/etc/passwd' }, standalone: false, safe: :safe)
+      output = Asciidoctor.convert(input, attributes: { 'kroki-plantuml-include' => '/etc/passwd' }, standalone: false, safe: :safe)
       (expect output).to eql %(<div class="imageblock kroki">
 <div class="content">
-<img src="https://kroki.io/plantuml/png/eNpLzMlMTlXQtVNIyk-yUshIzcnJBwA9iwZL" alt="Diagram">
+<img src="https://kroki.io/plantuml/svg/eNpLzMlMTlXQtVNIyk-yUshIzcnJBwA9iwZL" alt="Diagram">
 </div>
 </div>)
     end
@@ -83,10 +100,10 @@
         alice -> bob: hello
         ....
       ADOC
-      output = Asciidoctor.convert(input, attributes: { 'env-idea' => '', 'kroki-plantuml-include' => 'spec/fixtures/config.puml' }, standalone: false, safe: :secure)
+      output = Asciidoctor.convert(input, attributes: { 'kroki-plantuml-include' => 'spec/fixtures/config.puml' }, standalone: false, safe: :secure)
       (expect output).to eql %(<div class="imageblock kroki">
 <div class="content">
-<img src="https://kroki.io/plantuml/png/eNpLzMlMTlXQtVNIyk-yUshIzcnJBwA9iwZL" alt="Diagram">
+<img src="https://kroki.io/plantuml/svg/eNpLzMlMTlXQtVNIyk-yUshIzcnJBwA9iwZL" alt="Diagram">
 </div>
 </div>)
     end