diff --git a/jena-arq/src/main/java/org/apache/jena/sparql/core/assembler/DatasetAssembler.java b/jena-arq/src/main/java/org/apache/jena/sparql/core/assembler/DatasetAssembler.java
index db281ec028d..6b35c3e0c1b 100644
--- a/jena-arq/src/main/java/org/apache/jena/sparql/core/assembler/DatasetAssembler.java
+++ b/jena-arq/src/main/java/org/apache/jena/sparql/core/assembler/DatasetAssembler.java
@@ -32,6 +32,10 @@
 
 public abstract class DatasetAssembler extends AssemblerBase implements Assembler {
 
+    /** @deprecated To be removed - use {@link #getGeneralType()} */
+    @Deprecated
+    public static Resource getType() { return getGeneralType(); }
+
     /** This is the superclass of all datasets assemblers */
     public static Resource getGeneralType() {
         return DatasetAssemblerVocab.tDataset ;
diff --git a/jena-arq/src/test/java/org/apache/jena/riot/TestSysRIOT.java b/jena-arq/src/test/java/org/apache/jena/riot/TestSysRIOT.java
index 95118dc12b1..69593c84ecb 100644
--- a/jena-arq/src/test/java/org/apache/jena/riot/TestSysRIOT.java
+++ b/jena-arq/src/test/java/org/apache/jena/riot/TestSysRIOT.java
@@ -20,8 +20,6 @@
 
 import static org.apache.jena.atlas.lib.Lib.lowercase;
 
-import java.util.function.Predicate;
-
 import org.apache.jena.atlas.io.IO;
 import org.apache.jena.base.Sys;
 import org.junit.Assert;
@@ -43,7 +41,7 @@ public void chooseBaseIRI_2() {
     public void chooseBaseIRI_3() {
         if ( Sys.isWindows ) {
             if ( IO.exists("c:/") )
-                testChooseBaseIRI("c:", s->lowercase(s).startsWith("file:///c:/"));
+                testChooseBaseIRI_windows("c:/", "file:///c:/");
         } else
             testChooseBaseIRI("x:", "x:");
     }
@@ -52,14 +50,15 @@ public void chooseBaseIRI_3() {
     public void chooseBaseIRI_4() {
         if ( Sys.isWindows ) {
             if ( IO.exists("c:/") )
-                testChooseBaseIRI("c:", s->lowercase(s).startsWith("file:///c:/"));
+                testChooseBaseIRI_windows("c:", "file:///c:");
         } else
             testChooseBaseIRI("x:/", "x:/");
     }
 
     @Test
     public void chooseBaseIRI_10() {
-        testChooseBaseIRI("foo", s->s.startsWith("file:///"));
+        String x = SysRIOT.chooseBaseIRI(null, "foo");
+        Assert.assertTrue(x.startsWith("file:///"));
     }
 
     private void testChooseBaseIRI(String input, String expected) {
@@ -67,8 +66,13 @@ private void testChooseBaseIRI(String input, String expected) {
         Assert.assertEquals(expected, x);
     }
 
-    private void testChooseBaseIRI(String input, Predicate<String> test) {
+    private void testChooseBaseIRI_windows(String input, String prefix) {
         String x = SysRIOT.chooseBaseIRI(null, input);
-        Assert.assertTrue(test.test(x));
+        String x1 = lowercase(x);
+        boolean b = x1.startsWith(prefix);
+        if ( ! b )
+            System.out.printf("Input: %s => (prefix(%s)  A:%s)=\n", input, prefix, x1);
+        // drive letters can be uppercase.
+        Assert.assertTrue(x1.startsWith(prefix));
     }
 }
diff --git a/jena-base/src/test/java/org/apache/jena/atlas/lib/TestFilenameProcessing.java b/jena-base/src/test/java/org/apache/jena/atlas/lib/TestFilenameProcessing.java
index b83846c63d1..4476104ec19 100644
--- a/jena-base/src/test/java/org/apache/jena/atlas/lib/TestFilenameProcessing.java
+++ b/jena-base/src/test/java/org/apache/jena/atlas/lib/TestFilenameProcessing.java
@@ -26,6 +26,7 @@
 import java.io.File ;
 import java.nio.file.Path;
 
+import org.apache.jena.base.Sys;
 import org.junit.Test ;
 
 public class TestFilenameProcessing
@@ -37,7 +38,7 @@ public class TestFilenameProcessing
     // ---- Main tests.
     // Portablility
 
-    static boolean isWindows = File.separatorChar != '/' ;
+    static boolean isWindows = Sys.isWindows;
 
     private static String cwd = Path.of(".").toAbsolutePath().normalize().toString() ;
     // Sort out cwd, not using the IRILib code.
diff --git a/jena-base/src/test/java/org/apache/jena/atlas/lib/TestIRILib.java b/jena-base/src/test/java/org/apache/jena/atlas/lib/TestIRILib.java
index ee72e46e51b..dc260cd9c62 100644
--- a/jena-base/src/test/java/org/apache/jena/atlas/lib/TestIRILib.java
+++ b/jena-base/src/test/java/org/apache/jena/atlas/lib/TestIRILib.java
@@ -22,6 +22,9 @@
 
 import org.junit.Test;
 
+/*
+ * @see TestFilenameProcessing
+ */
 public class TestIRILib {
 
     @Test public void encodeDecode01() { encodeDecode("", ""); }
diff --git a/jena-core/src/main/java/org/apache/jena/irix/IRIs.java b/jena-core/src/main/java/org/apache/jena/irix/IRIs.java
index 38149142b3f..b9890e41da8 100644
--- a/jena-core/src/main/java/org/apache/jena/irix/IRIs.java
+++ b/jena-core/src/main/java/org/apache/jena/irix/IRIs.java
@@ -84,8 +84,10 @@ public static String toBase(String uriForBase) {
         String scheme = scheme(uriForBase);
         if ( Sys.isWindows ) {
             // Assume a scheme of one letter is a Windows drive letter.
-            if ( scheme != null && scheme.length() == 1 )
+            if ( scheme != null && scheme.length() == 1 ) {
                 scheme = "file";
+                uriForBase = "file:/"+uriForBase;
+            }
         }
         if ( scheme == null  ) {
             // Relative name: it the base is a file: URI, encode the relative