diff --git a/jsign-core/src/main/java/net/jsign/KeyStoreBuilder.java b/jsign-core/src/main/java/net/jsign/KeyStoreBuilder.java
index 4ab4bc5e..cede7b38 100644
--- a/jsign-core/src/main/java/net/jsign/KeyStoreBuilder.java
+++ b/jsign-core/src/main/java/net/jsign/KeyStoreBuilder.java
@@ -136,7 +136,11 @@ KeyStoreType storetype() {
                 storetype = NONE;
             } else {
                 // the keystore type wasn't specified, let's try to guess it
-                storetype = KeyStoreType.of(createFile(keystore));
+                File file = createFile(keystore);
+                if (!file.isFile()) {
+                    throw new IllegalArgumentException("Keystore file '" + keystore + "' not found");
+                }
+                storetype = KeyStoreType.of(file);
                 if (storetype == null) {
                     throw new IllegalArgumentException("Keystore type of '" + keystore + "' not recognized");
                 }
diff --git a/jsign-core/src/test/java/net/jsign/KeyStoreBuilderTest.java b/jsign-core/src/test/java/net/jsign/KeyStoreBuilderTest.java
index 25cf85a8..715ab881 100644
--- a/jsign-core/src/test/java/net/jsign/KeyStoreBuilderTest.java
+++ b/jsign-core/src/test/java/net/jsign/KeyStoreBuilderTest.java
@@ -415,6 +415,34 @@ public void testBuildPKCS12() throws Exception {
         assertNotNull("keystore", keystore);
     }
 
+    @Test
+    public void testBuildWithoutStoreType() throws Exception {
+        KeyStoreBuilder builder = new KeyStoreBuilder();
+
+        try {
+            builder.build();
+            fail("Exception not thrown");
+        } catch (IllegalArgumentException e) {
+            assertEquals("message", "Either keystore, or keyfile and certfile, or storetype parameters must be set", e.getMessage());
+        }
+
+        builder.keystore("target/test-classes/keystores/keystore.error");
+
+        try {
+            builder.build();
+            fail("Exception not thrown");
+        } catch (IllegalArgumentException e) {
+            assertEquals("message", "Keystore file 'target/test-classes/keystores/keystore.error' not found", e.getMessage());
+        }
+
+        builder.keystore("target/test-classes/keystores/keystore.p12");
+
+        assertEquals("storetype", PKCS12, builder.storetype());
+
+        KeyStore keystore = builder.build();
+        assertNotNull("keystore", keystore);
+    }
+
     @Test
     public void testBuildPKCS11() throws Exception {
         KeyStoreBuilder builder = new KeyStoreBuilder().storetype(PKCS11);