diff --git a/build.gradle b/build.gradle
index 7a04bad..c88fd88 100644
--- a/build.gradle
+++ b/build.gradle
@@ -70,34 +70,35 @@ tasks.register('downloadTestData') {
     }
 }
 
-tasks.register('testPreferred', Test) {
+tasks.register('test256', Test) {
     dependsOn downloadTestData
     useJUnitPlatform()
     jvmArgs += [
             '--add-modules', 'jdk.incubator.vector',
-            '-Xmx2g'
+            '-Xmx2g',
+            '-Dorg.simdjson.species=256'
     ]
     testLogging {
         events 'PASSED', 'SKIPPED', 'FAILED', 'STANDARD_OUT', 'STANDARD_ERROR'
     }
 }
 
-tasks.register('test256', Test) {
+tasks.register('test512', Test) {
     dependsOn downloadTestData
     useJUnitPlatform()
-    onlyIf() {
-        ByteVector.SPECIES_PREFERRED == ByteVector.SPECIES_512 
-    }
     jvmArgs += [
             '--add-modules', 'jdk.incubator.vector',
             '-Xmx2g',
-            '-XX:UseAVX=2'
+            '-Dorg.simdjson.species=512'
     ]
+    testLogging {
+        events 'PASSED', 'SKIPPED', 'FAILED', 'STANDARD_OUT', 'STANDARD_ERROR'
+    }
 }
 
 test {
-    dependsOn 'testPreferred'
     dependsOn 'test256'
+    dependsOn 'test512'
 }
 
 tasks.withType(JmhBytecodeGeneratorTask).configureEach {
diff --git a/src/main/java/org/simdjson/StructuralIndexer.java b/src/main/java/org/simdjson/StructuralIndexer.java
index cb0201e..c0eb4b0 100644
--- a/src/main/java/org/simdjson/StructuralIndexer.java
+++ b/src/main/java/org/simdjson/StructuralIndexer.java
@@ -12,7 +12,13 @@ class StructuralIndexer {
     static final int N_CHUNKS;
 
     static {
-        SPECIES = ByteVector.SPECIES_PREFERRED;
+        String species = System.getProperty("org.simdjson.species", "preferred");
+        SPECIES = switch(species) {
+            case "preferred" -> ByteVector.SPECIES_PREFERRED;
+            case "512" -> ByteVector.SPECIES_512;      
+            case "256" -> ByteVector.SPECIES_256;
+            default -> throw new IllegalArgumentException("Unsupported vector species: " + species);
+        };              
         N_CHUNKS = 64 / SPECIES.vectorByteSize();
         if (SPECIES != ByteVector.SPECIES_256 && SPECIES != ByteVector.SPECIES_512) {
             throw new IllegalArgumentException("Unsupported vector species: " + SPECIES);