diff --git a/asciidoctor-gradle-base/src/main/groovy/org/asciidoctor/gradle/base/AsciidoctorUtils.groovy b/asciidoctor-gradle-base/src/main/groovy/org/asciidoctor/gradle/base/AsciidoctorUtils.groovy
index 2f26368b3..07aa59968 100644
--- a/asciidoctor-gradle-base/src/main/groovy/org/asciidoctor/gradle/base/AsciidoctorUtils.groovy
+++ b/asciidoctor-gradle-base/src/main/groovy/org/asciidoctor/gradle/base/AsciidoctorUtils.groovy
@@ -36,7 +36,7 @@ import static groovy.lang.Closure.DELEGATE_FIRST
 class AsciidoctorUtils {
 
     public static final OperatingSystem OS = OperatingSystem.current()
-    public static final String UNDERSCORE_LED_FILES = '**/_*'
+    public static final String UNDERSCORE_LED_FILES = '**/_*.a*'
 
     static final Spec<? super File> ACCEPT_ONLY_FILES = new Spec<File>() {
         @Override
diff --git a/asciidoctor-gradle-jvm/src/main/groovy/org/asciidoctor/gradle/jvm/AbstractAsciidoctorTask.groovy b/asciidoctor-gradle-jvm/src/main/groovy/org/asciidoctor/gradle/jvm/AbstractAsciidoctorTask.groovy
index 496723560..1a83f8011 100644
--- a/asciidoctor-gradle-jvm/src/main/groovy/org/asciidoctor/gradle/jvm/AbstractAsciidoctorTask.groovy
+++ b/asciidoctor-gradle-jvm/src/main/groovy/org/asciidoctor/gradle/jvm/AbstractAsciidoctorTask.groovy
@@ -739,21 +739,16 @@ class AbstractAsciidoctorTask extends DefaultTask {
      */
     @Internal
     protected PatternSet getDefaultSourceDocumentPattern() {
-        PatternSet ps = new PatternSet()
-        ps.include '**/*.adoc'
-        ps.include '**/*.ad'
-        ps.include '**/*.asc'
-        ps.include '**/*.asciidoc'
-        ps.exclude UNDERSCORE_LED_FILES
+        asciidocPatterns.exclude UNDERSCORE_LED_FILES
     }
 
     /** The default pattern set for secondary sources.
      *
-     * @return {@link #getDefaultSourceDocumentPattern} + `*docinfo*`.
+     * @return {@link #getDefaultSourceDocumentPattern} + {@code _*.adoc}.
      */
     @Internal
     protected PatternSet getDefaultSecondarySourceDocumentPattern() {
-        defaultSourceDocumentPattern
+        asciidocPatterns
     }
 
     /** The default CopySpec that will be used if {@code resources} was never called
@@ -1147,4 +1142,12 @@ class AbstractAsciidoctorTask extends DefaultTask {
                 project.configurations.getByName(StringUtils.stringize(sourceConfig))
         }
     }
+
+    private PatternSet getAsciidocPatterns() {
+        PatternSet ps = new PatternSet()
+        ps.include '**/*.adoc'
+        ps.include '**/*.ad'
+        ps.include '**/*.asc'
+        ps.include '**/*.asciidoc'
+    }
 }