diff --git a/financer-server/src/main/java/de/financer/service/TransactionService.java b/financer-server/src/main/java/de/financer/service/TransactionService.java
index ffb173b..ba6de63 100644
--- a/financer-server/src/main/java/de/financer/service/TransactionService.java
+++ b/financer-server/src/main/java/de/financer/service/TransactionService.java
@@ -80,7 +80,10 @@ public class TransactionService {
                     buildTransaction(fromAccount, toAccount, amount, description, date, recurringTransaction, taxRelevant);
 
             transaction.setPeriods(getRelevantPeriods(transaction));
-            transaction.setFiles(Collections.singleton(buildFile(fileName, fileContent)));
+
+            if (StringUtils.isNotEmpty(fileName) && StringUtils.isNotEmpty(fileContent)) {
+                transaction.setFiles(Collections.singleton(buildFile(fileName, fileContent)));
+            }
 
             fromAccount.setCurrentBalance(fromAccount.getCurrentBalance() + (this.ruleService
                     .getMultiplierFromAccount(fromAccount) * amount));
diff --git a/financer-web-client/pom.xml b/financer-web-client/pom.xml
index f8cb964..e6c201b 100644
--- a/financer-web-client/pom.xml
+++ b/financer-web-client/pom.xml
@@ -54,6 +54,11 @@
             <artifactId>jfreechart</artifactId>
             <version>1.5.0</version>
         </dependency>
+        <dependency>
+            <groupId>org.overviewproject</groupId>
+            <artifactId>mime-types</artifactId>
+            <version>0.1.3</version>
+        </dependency>
 
         <!-- Financer dependencies -->
         <dependency>
diff --git a/financer-web-client/src/main/java/de/financer/controller/FileController.java b/financer-web-client/src/main/java/de/financer/controller/FileController.java
index 5d26b04..0e4fcfb 100644
--- a/financer-web-client/src/main/java/de/financer/controller/FileController.java
+++ b/financer-web-client/src/main/java/de/financer/controller/FileController.java
@@ -5,6 +5,8 @@ import de.financer.model.File;
 import de.financer.template.FinancerRestTemplate;
 import de.financer.template.exception.FinancerRestException;
 import de.financer.util.ControllerUtils;
+import org.overviewproject.mime_types.GetBytesException;
+import org.overviewproject.mime_types.MimeTypeDetector;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.core.io.ByteArrayResource;
 import org.springframework.core.io.Resource;
@@ -36,8 +38,20 @@ public class FileController {
             return null;
         }
 
+        final byte[] decodedFileContent = Base64.getDecoder().decode(file.getContent());
+
         return ResponseEntity.ok()
                              .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + file.getName() + "\"")
-                             .body(new ByteArrayResource(Base64.getDecoder().decode(file.getContent())));
+                             .header(HttpHeaders.CONTENT_TYPE, getMimeTypeForFile(file.getName(), decodedFileContent))
+                             .header(HttpHeaders.CONTENT_LENGTH, String.valueOf(decodedFileContent.length))
+                             .body(new ByteArrayResource(decodedFileContent));
+    }
+
+    private String getMimeTypeForFile(String fileName, byte[] content) {
+        try {
+            return new MimeTypeDetector().detectMimeType(fileName, () -> content);
+        } catch(GetBytesException e) {
+            return "text/html";
+        }
     }
 }
diff --git a/financer-web-client/src/main/java/de/financer/controller/TransactionController.java b/financer-web-client/src/main/java/de/financer/controller/TransactionController.java
index 9c76853..c5b0f16 100644
--- a/financer-web-client/src/main/java/de/financer/controller/TransactionController.java
+++ b/financer-web-client/src/main/java/de/financer/controller/TransactionController.java
@@ -11,6 +11,7 @@ import de.financer.form.NewTransactionForm;
 import de.financer.model.Account;
 import de.financer.template.exception.FinancerRestException;
 import de.financer.util.ControllerUtils;
+import org.apache.commons.lang3.StringUtils;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.stereotype.Controller;
@@ -119,7 +120,7 @@ public class TransactionController {
         requestDto.setDescription(form.getDescription());
         requestDto.setTaxRelevant(form.getTaxRelevant());
 
-        if (form.getFile() != null) {
+        if (form.getFile() != null && StringUtils.isNotEmpty(form.getFile().getOriginalFilename())) {
             try {
                 requestDto.setFileContent(Base64.getEncoder().encodeToString(form.getFile().getBytes()));
                 requestDto.setFileName(form.getFile().getOriginalFilename());
diff --git a/financer-web-client/src/main/resources/static/changelog.txt b/financer-web-client/src/main/resources/static/changelog.txt
index e82bf46..f9bf258 100644
--- a/financer-web-client/src/main/resources/static/changelog.txt
+++ b/financer-web-client/src/main/resources/static/changelog.txt
@@ -1,3 +1,7 @@
+v29 -> v30:
+- Fix a bug in the file upload feature that caused every transaction to have a file, even though no file was uploaded
+- Set proper HTTP headers for file download (mime type, length)
+
 v28 -> v29:
 - Internal optimizations