diff --git a/cloud-core/src/main/java/cloud/commandframework/arguments/standard/BooleanArgument.java b/cloud-core/src/main/java/cloud/commandframework/arguments/standard/BooleanArgument.java
index 5764a43b..179e8bc5 100644
--- a/cloud-core/src/main/java/cloud/commandframework/arguments/standard/BooleanArgument.java
+++ b/cloud-core/src/main/java/cloud/commandframework/arguments/standard/BooleanArgument.java
@@ -34,9 +34,11 @@ import cloud.commandframework.exceptions.parsing.NoInputProvidedException;
 import cloud.commandframework.exceptions.parsing.ParserException;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Locale;
 import java.util.Objects;
 import java.util.Queue;
 import java.util.function.BiFunction;
+import java.util.stream.Collectors;
 import org.apiguardian.api.API;
 import org.checkerframework.checker.nullness.qual.NonNull;
 import org.checkerframework.checker.nullness.qual.Nullable;
@@ -162,10 +164,16 @@ public final class BooleanArgument<C> extends CommandArgument<C, Boolean> {
     @API(status = API.Status.STABLE)
     public static final class BooleanParser<C> implements ArgumentParser<C, Boolean> {
 
+        private static final List<String> STRICT = Arrays.asList("TRUE", "FALSE");
         private static final List<String> LIBERAL = Arrays.asList("TRUE", "YES", "ON", "FALSE", "NO", "OFF");
         private static final List<String> LIBERAL_TRUE = Arrays.asList("TRUE", "YES", "ON");
         private static final List<String> LIBERAL_FALSE = Arrays.asList("FALSE", "NO", "OFF");
 
+        private static final List<String> STRICT_LOWER = STRICT
+                .stream().map(s -> s.toLowerCase(Locale.ROOT)).collect(Collectors.toList());
+        private static final List<String> LIBERAL_LOWER = LIBERAL
+                .stream().map(s -> s.toLowerCase(Locale.ROOT)).collect(Collectors.toList());
+
         private final boolean liberal;
 
         /**
@@ -225,10 +233,10 @@ public final class BooleanArgument<C> extends CommandArgument<C, Boolean> {
                 final @NonNull String input
         ) {
             if (!this.liberal) {
-                return Arrays.asList("TRUE", "FALSE");
+                return STRICT_LOWER;
             }
 
-            return LIBERAL;
+            return LIBERAL_LOWER;
         }
 
         @Override
diff --git a/cloud-core/src/test/java/cloud/commandframework/arguments/standard/BooleanParserTest.java b/cloud-core/src/test/java/cloud/commandframework/arguments/standard/BooleanParserTest.java
index 3fb63e6f..f5bff39f 100644
--- a/cloud-core/src/test/java/cloud/commandframework/arguments/standard/BooleanParserTest.java
+++ b/cloud-core/src/test/java/cloud/commandframework/arguments/standard/BooleanParserTest.java
@@ -148,8 +148,8 @@ class BooleanParserTest {
 
     static Stream<Arguments> Suggestions_ExpectedSuggestions_Source() {
         return Stream.of(
-                Arguments.arguments(false, ArgumentTestHelper.linkedListOf("TRUE", "FALSE")),
-                Arguments.arguments(true, ArgumentTestHelper.linkedListOf("TRUE", "YES", "ON", "FALSE", "NO", "OFF"))
+                Arguments.arguments(false, ArgumentTestHelper.linkedListOf("true", "false")),
+                Arguments.arguments(true, ArgumentTestHelper.linkedListOf("true", "yes", "on", "false", "no", "off"))
         );
     }
 }