diff --git a/main/src/com/google/refine/importers/TextFormatGuesser.java b/main/src/com/google/refine/importers/TextFormatGuesser.java
index d607340df..a5c8f072b 100644
--- a/main/src/com/google/refine/importers/TextFormatGuesser.java
+++ b/main/src/com/google/refine/importers/TextFormatGuesser.java
@@ -74,7 +74,7 @@ public class TextFormatGuesser implements FormatGuesser {
                 String line;
                 while ((line = reader.readLine()) != null && controls < CONTROLS_THRESHOLD) {
                     line = line.trim();
-                    controls += CharMatcher.javaIsoControl().countIn(line);
+                    controls += CharMatcher.javaIsoControl().and(CharMatcher.whitespace().negate()).countIn(line);
                     openBraces += line.chars().filter(ch -> ch == '{').count();
                     closeBraces += StringUtils.countMatches(line, "}");
                     openAngleBrackets += StringUtils.countMatches(line, "<");
diff --git a/main/tests/server/src/com/google/refine/importers/TextFormatGuesserTests.java b/main/tests/server/src/com/google/refine/importers/TextFormatGuesserTests.java
index a159bb9e6..adf3ff4c4 100644
--- a/main/tests/server/src/com/google/refine/importers/TextFormatGuesserTests.java
+++ b/main/tests/server/src/com/google/refine/importers/TextFormatGuesserTests.java
@@ -83,6 +83,7 @@ public class TextFormatGuesserTests extends ImporterTest {
 
     @Test
     public void xlsTextGuessTest() throws FileNotFoundException, IOException {
+        // Test an XLSX file without the correct file extension
         String dir = ClassLoader.getSystemResource("Colorado-Municipalities-small-xlsx.gz").getPath();
         InputStream is = new GZIPInputStream(new FileInputStream(new File(dir)));
         File tmp = File.createTempFile("openrefinetests-textguesser", "");
@@ -96,6 +97,11 @@ public class TextFormatGuesserTests extends ImporterTest {
         extensionGuesserTests("csv", "text/line-based");
     }
 
+    @Test
+    public void tsvGuesserTest() {
+        extensionGuesserTests("tsv", "text/line-based");
+    }
+
     @Test(enabled=false) // FIXME: Our JSON guesser doesn't work on small files
     public void jsonGuesserTest() {
         extensionGuesserTests("json", "text/json");
@@ -112,8 +118,7 @@ public class TextFormatGuesserTests extends ImporterTest {
         File testDataDir =  new File(dir);
         for (String testFile : testDataDir.list(new PatternFilenameFilter(".+\\." + extension))) {
             String format = guesser.guess(new File(dir, testFile), "UTF-8", "text");
-            logger.info(format + " " + testFile);
-            assertEquals(format, expectedFormat);
+            assertEquals(format, expectedFormat, "Format guess failed for " + testFile);
         }
     }