diff --git a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/service/TargetFilenameBuildingService.java b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/service/TargetFilenameBuildingService.java
index 4641da3..88d5d6a 100644
--- a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/service/TargetFilenameBuildingService.java
+++ b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/service/TargetFilenameBuildingService.java
@@ -91,16 +91,16 @@ public final class TargetFilenameBuildingService {
      * <ul>
      *   <li>Resolved date must be non-null.</li>
      *   <li>Validated title must be non-null and non-blank.</li>
-     *   <li>Validated title must not exceed 20 characters.</li>
-     *   <li>Validated title must contain only letters, digits, and spaces.</li>
+     *   <li>Validated title must not exceed 20 characters (before Windows cleaning).</li>
+     *   <li>After Windows-character cleaning, title must contain only letters, digits, and spaces.</li>
      * </ul>
      * If any rule is violated, the state is treated as an
      * {@link InconsistentProposalState}.
      * <p>
-     * Windows compatibility: The final filename is cleaned of Windows-incompatible characters
-     * (e.g., {@code < > : " / \ | ? *}) to ensure the resulting filename can be created on
-     * Windows systems. This is a defensive measure; the validated title is already expected
-     * to contain only letters, digits, and spaces.
+     * Windows compatibility: Windows-incompatible characters
+     * (e.g., {@code < > : " / \ | ? *}) are removed from the title before final validation.
+     * This ensures the resulting filename can be created on Windows systems.
+     * The 20-character rule is applied to the original title before cleaning.
      * <p>
      * The 20-character limit applies exclusively to the base title. A duplicate-avoidance
      * suffix (e.g., {@code (1)}) may be appended by the target folder adapter after this
@@ -132,21 +132,23 @@ public final class TargetFilenameBuildingService {
                             + title + "'");
         }
 
-        if (!isAllowedTitleCharacters(title)) {
-            return new InconsistentProposalState(
-                    "Leading PROPOSAL_READY attempt has title with disallowed characters "
-                            + "(only letters, digits, and spaces are permitted): '"
-                            + title + "'");
-        }
-
-        // Defensive Windows compatibility: remove Windows-incompatible characters
+        // Remove Windows-incompatible characters to enable technical Windows compatibility
         String cleanedTitle = removeWindowsIncompatibleCharacters(title);
+
         if (cleanedTitle.isBlank()) {
             return new InconsistentProposalState(
                     "Title becomes empty after Windows-compatibility cleaning: '"
                             + title + "'");
         }
 
+        // After cleaning, verify that only letters, digits, and spaces remain
+        if (!isAllowedTitleCharacters(cleanedTitle)) {
+            return new InconsistentProposalState(
+                    "After Windows-compatibility cleaning, title contains disallowed characters "
+                            + "(only letters, digits, and spaces are permitted): '"
+                            + cleanedTitle + "'");
+        }
+
         // Build: YYYY-MM-DD - Titel.pdf
         String baseFilename = date + " - " + cleanedTitle + ".pdf";
         return new BaseFilenameReady(baseFilename);
diff --git a/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/service/TargetFilenameBuildingServiceTest.java b/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/service/TargetFilenameBuildingServiceTest.java
index 0b1e49e..e70ffca 100644
--- a/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/service/TargetFilenameBuildingServiceTest.java
+++ b/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/service/TargetFilenameBuildingServiceTest.java
@@ -202,16 +202,35 @@ class TargetFilenameBuildingServiceTest {
     }
 
     @Test
-    void buildBaseFilename_titleWithSlash_returnsInconsistentProposalState() {
+    void buildBaseFilename_titleWithSlash_removesWindowsIncompatibleCharacterAndSucceeds() {
+        // Slash (/) is a Windows-incompatible character. It should be removed,
+        // leaving "RgStrom" which is valid (letters only)
         ProcessingAttempt attempt = proposalAttempt(LocalDate.of(2026, 1, 1), "Rg/Strom");
 
         BaseFilenameResult result = TargetFilenameBuildingService.buildBaseFilename(attempt);
 
-        assertThat(result).isInstanceOf(InconsistentProposalState.class);
+        assertThat(result).isInstanceOf(BaseFilenameReady.class);
+        assertThat(((BaseFilenameReady) result).baseFilename())
+                .isEqualTo("2026-01-01 - RgStrom.pdf");
+    }
+
+    @Test
+    void buildBaseFilename_titleWithMultipleWindowsChars_removesAllAndSucceeds() {
+        // Multiple Windows-incompatible characters (: and ") should be removed,
+        // leaving "Rechnung 2026" which is valid (letters, digits, and spaces)
+        ProcessingAttempt attempt = proposalAttempt(LocalDate.of(2026, 1, 1), "Rechnung: \"2026\"");
+
+        BaseFilenameResult result = TargetFilenameBuildingService.buildBaseFilename(attempt);
+
+        assertThat(result).isInstanceOf(BaseFilenameReady.class);
+        assertThat(((BaseFilenameReady) result).baseFilename())
+                .isEqualTo("2026-01-01 - Rechnung 2026.pdf");
     }
 
     @Test
     void buildBaseFilename_titleWithDot_returnsInconsistentProposalState() {
+        // Dot (.) is NOT a Windows-incompatible character (as per our list < > : " / \ | ? *)
+        // So it remains in the cleaned title and causes validation to fail
         ProcessingAttempt attempt = proposalAttempt(LocalDate.of(2026, 1, 1), "Rechnung.pdf");
 
         BaseFilenameResult result = TargetFilenameBuildingService.buildBaseFilename(attempt);