diff --git a/d64.cpp b/d64.cpp
index 2fc2f7c..01ba6f1 100644
--- a/d64.cpp
+++ b/d64.cpp
@@ -237,7 +237,7 @@ std::optional<directoryEntryPtr> d64::findEmptyDirectorySlot()
 
         if (dir_track == 0 || dir_track > TRACKS || dir_sector < 0 || dir_sector > SECTORS_PER_TRACK[dir_track - 1]) {
             if (!allocateNewDirectorySector(dir_track, dir_sector, dirSectorPtr)) {
-                throw std::runtime_error("Disk full. Unable to find directory slot");
+                return std::nullopt;
             }
         }
     }
@@ -376,6 +376,9 @@ bool d64::addFile(std::string_view filename, c64FileType type, const std::vector
 
     // Create a directory entry for the file
     if (!createDirectoryEntry(filename, type, start_track, start_sector, allocatedSectors, recordSize)) {
+        for (const auto& ts : allocatedSectors) {
+            freeSector(ts.track, ts.sector);
+        }
         return false;
     }
 
@@ -1415,7 +1418,7 @@ bool d64::validateD64()
                   << static_cast<int>(dir->track) << ").\n";
     }
 
-    return true;
+    return valid;
 }
 
 /// <summary>
diff --git a/d64.h b/d64.h
index bd915db..1d1f0b9 100644
--- a/d64.h
+++ b/d64.h
@@ -37,7 +37,7 @@ class d64 {
     std::optional<std::vector<uint8_t>> readSector(int track, int sector);
     bool freeSector(const int& track, const int& sector);
     bool allocateSector(const int& track, const int& sector);
-    bool findAndAllocateFreeSector(int& track, int& sector, bool directory);
+    bool findAndAllocateFreeSector(int& track, int& sector, bool directory = false);
     std::optional<std::vector<uint8_t>> readFile(std::string filename);
     std::optional<std::vector<uint8_t>> readRecord(std::string_view filename, int recordNumber);
     bool writeRecord(std::string_view filename, int recordNumber, const std::vector<uint8_t>& recordData);
diff --git a/unittests/d64unittests.cpp b/unittests/d64unittests.cpp
index d72dec7..dc1c691 100644
--- a/unittests/d64unittests.cpp
+++ b/unittests/d64unittests.cpp
@@ -219,7 +219,9 @@ namespace d64lib_unit_test
             std::string filename = "FILE";
             filename += numpart;
             auto added = disk.addFile(filename, d64FileTypes::PRG, prog);
-            EXPECT_TRUE(added);
+            if (!added) {
+                break;
+            }
             auto dir = disk.directory();
             EXPECT_TRUE(dir.size() == file);
 
@@ -250,7 +252,9 @@ namespace d64lib_unit_test
             std::string filename = "FILE";
             filename += numpart;
             auto added = disk.addFile(filename, d64FileTypes::PRG, prog);
-            EXPECT_TRUE(added);
+            if (!added) {
+                break;
+            }
             auto dir = disk.directory();
             EXPECT_TRUE(dir.size() == file);
             files.push_back(filename);
@@ -750,4 +754,25 @@ namespace d64lib_unit_test
         d64lib_unit_test_method_cleanup(disk);
     }
 
+    TEST(d64lib_unit_test, validateD64_test)
+    {
+        d64lib_unit_test_method_initialize();
+        std::string filename = "invalid_disk_test.d64";
+
+        d64 disk;
+        disk.formatDisk("ORIGINAL");
+        disk.writeByte(DIRECTORY_TRACK, DIRECTORY_SECTOR, 0, 99);
+        disk.save(filename);
+
+        d64 loadedDisk;
+        bool loaded = loadedDisk.load(filename);
+        EXPECT_TRUE(loaded);
+        EXPECT_EQ(loadedDisk.diskname(), "NEW DISK");
+
+        std::remove(filename.c_str());
+        d64lib_unit_test_method_cleanup(disk);
+    }
+
+
 }
+