diff --git a/scim-core/src/test/java/org/apache/directory/scim/core/repository/PatchHandlerTest.java b/scim-core/src/test/java/org/apache/directory/scim/core/repository/PatchHandlerTest.java
index ac9e384a..a77ba00e 100644
--- a/scim-core/src/test/java/org/apache/directory/scim/core/repository/PatchHandlerTest.java
+++ b/scim-core/src/test/java/org/apache/directory/scim/core/repository/PatchHandlerTest.java
@@ -250,6 +250,48 @@ public void applyRemoveItemWithFilter() {
     assertThat(updatedUser.getAddresses().get(0).getPostalCode()).isEqualTo("43210");
   }
 
+  @Test
+  public void applyPrimaryString() {
+    ScimUser user = user().setAddresses(List.of(
+      new Address()
+        .setType("work")
+        .setStreetAddress("101 Main Street")
+        .setRegion("Springfield")
+        .setPostalCode("01234")
+        .setPrimary(true),
+      new Address()
+        .setType("home")
+        .setStreetAddress("202 Maple Street")
+        .setRegion("Otherton")
+        .setPostalCode("43210")
+        .setPrimary(false)
+    ));
+
+    PatchOperation op = patchOperation(REPLACE, "addresses[primary EQ true].postalCode", "32140");
+    ScimUser updatedUser = patchHandler.apply(user, List.of(op));
+    assertThat(updatedUser.getAddresses().size()).isEqualTo(2);
+    assertThat(updatedUser.getAddresses().get(0).getPostalCode()).isEqualTo("32140");
+    assertThat(updatedUser.getAddresses().get(1).getPostalCode()).isEqualTo("43210");
+
+    op = patchOperation(REPLACE, "addresses[primary EQ \"True\"].postalCode", "42");
+    updatedUser = patchHandler.apply(user, List.of(op));
+    assertThat(updatedUser.getAddresses().size()).isEqualTo(2);
+    assertThat(updatedUser.getAddresses().get(0).getPostalCode()).isEqualTo("42");
+    assertThat(updatedUser.getAddresses().get(1).getPostalCode()).isEqualTo("43210");
+
+    op = patchOperation(REPLACE, "addresses[primary EQ false].postalCode", "1337");
+    updatedUser = patchHandler.apply(user, List.of(op));
+    assertThat(updatedUser.getAddresses().size()).isEqualTo(2);
+    assertThat(updatedUser.getAddresses().get(0).getPostalCode()).isEqualTo("01234");
+    assertThat(updatedUser.getAddresses().get(1).getPostalCode()).isEqualTo("1337");
+
+    op = patchOperation(REPLACE, "addresses[primary EQ \"False\"].postalCode", "7331");
+    updatedUser = patchHandler.apply(user, List.of(op));
+    assertThat(updatedUser.getAddresses().size()).isEqualTo(2);
+    assertThat(updatedUser.getAddresses().get(0).getPostalCode()).isEqualTo("01234");
+    assertThat(updatedUser.getAddresses().get(1).getPostalCode()).isEqualTo("7331");
+ }
+
   @Test
   public void applyRemoveAttributeWithFilter() {
     Address workAddress = new Address()
diff --git a/scim-spec/scim-spec-schema/src/main/java/org/apache/directory/scim/spec/filter/InMemoryScimFilterMatcher.java b/scim-spec/scim-spec-schema/src/main/java/org/apache/directory/scim/spec/filter/InMemoryScimFilterMatcher.java
index 049aec70..471d2b79 100644
--- a/scim-spec/scim-spec-schema/src/main/java/org/apache/directory/scim/spec/filter/InMemoryScimFilterMatcher.java
+++ b/scim-spec/scim-spec-schema/src/main/java/org/apache/directory/scim/spec/filter/InMemoryScimFilterMatcher.java
@@ -28,6 +28,7 @@
 
 import java.util.Collection;
 import java.util.Comparator;
+import java.util.Locale;
 import java.util.function.Predicate;
 
 class InMemoryScimFilterMatcher<R> extends BaseFilterExpressionMapper<Predicate<R>> {
@@ -181,17 +182,10 @@ protected boolean test(Schema.Attribute attribute, Object actualValue) {
       Object compareValue = expression.getCompareValue();
 
       if (op == CompareOperator.EQ) {
-
-        if (isStringExpression(attribute, compareValue) && !attribute.isCaseExact()) {
-          return actualValue.toString().equalsIgnoreCase(compareValue.toString());
-        }
-        return compareValue.equals(actualValue);
+        return eq(attribute, actualValue, compareValue);
       }
       if (op == CompareOperator.NE) {
-        if (isStringExpression(attribute, compareValue) && !attribute.isCaseExact()) {
-          return !actualValue.toString().equalsIgnoreCase(compareValue.toString());
-        }
-        return !compareValue.equals(actualValue);
+        return !eq(attribute, actualValue, compareValue);
       }
       if (op == CompareOperator.SW) {
         return isStringExpression(attribute, compareValue)
@@ -213,6 +207,30 @@ protected boolean test(Schema.Attribute attribute, Object actualValue) {
 
       throw new ScimResourceInvalidException("Unsupported operation in filter: " + op.name());
     }
+
+    private boolean eq(Schema.Attribute attribute, Object actualValue, Object compareValue)
+    {
+      if (isBooleanStringComparison(attribute, compareValue) || (isStringExpression(attribute, compareValue) && !attribute.isCaseExact())) {
+        return actualValue.toString().equalsIgnoreCase(compareValue.toString());
+      }
+      return compareValue.equals(actualValue);
+    }
+
+    private boolean isBooleanStringComparison(Schema.Attribute attribute, Object compareValue)
+    {
+      // Microsoft's SCIM Validator at https://scimvalidator.microsoft.com/ has patch operations
+      // with expressions like [primary EQ "True"]...
+      if (!attribute.getType().equals(Schema.Attribute.Type.BOOLEAN)) {
+        return false;
+      }
+
+      if (compareValue instanceof String compareValueString) {
+        String lowerCaseCompareValueString = compareValueString.toLowerCase(Locale.ROOT);
+        return "true".equals(lowerCaseCompareValueString) || "false".equals(lowerCaseCompareValueString);
+      }
+
+      return false;
+    }
   }
 
   private static class CompareOperatorPredicate<T> implements Predicate<T> {