diff --git a/src/GEval/BIO.hs b/src/GEval/BIO.hs
index f213ab4..7b7b601 100644
--- a/src/GEval/BIO.hs
+++ b/src/GEval/BIO.hs
@@ -93,7 +93,7 @@ bioLabelParser =
   (string "O" *> pure Outside) <|>
   (do
       labelType <- bioMarkerParser
-      string "-"
+      (string "-" <|> string "_")
       label <- takeWhile1 (\c -> not (isSpace c) && c /= '/')
       normalized <- (do
                        string "/"
diff --git a/test/Spec.hs b/test/Spec.hs
index b8dac23..83572e6 100644
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -259,6 +259,8 @@ main = hspec $ do
       runGEvalTest "bio-f1-complex" `shouldReturnAlmost` 0.625
     it "calculate F1" $ do
       runGEvalTest "bio-f1-simple" `shouldReturnAlmost` 0.5
+    it "calculate F1 with underscores rather than minus signs" $ do
+      runGEvalTest "bio-f1-simple-underscores" `shouldReturnAlmost` 0.5
     it "check perfect score" $ do
       runGEvalTest "bio-f1-perfect" `shouldReturnAlmost` 1.0
     it "check inconsistent input" $ do
diff --git a/test/bio-f1-simple-underscores/bio-f1-simple-underscores-solution/test-A/out.tsv b/test/bio-f1-simple-underscores/bio-f1-simple-underscores-solution/test-A/out.tsv
new file mode 100644
index 0000000..4380412
--- /dev/null
+++ b/test/bio-f1-simple-underscores/bio-f1-simple-underscores-solution/test-A/out.tsv
@@ -0,0 +1,3 @@
+O O B_city/POZNAŃ O O B_date/MARCH I_date/12
+B_city/BUK O O O
+B_name/FOO O B_surname/KOWALSKI
diff --git a/test/bio-f1-simple-underscores/bio-f1-simple-underscores/config.txt b/test/bio-f1-simple-underscores/bio-f1-simple-underscores/config.txt
new file mode 100644
index 0000000..70977e1
--- /dev/null
+++ b/test/bio-f1-simple-underscores/bio-f1-simple-underscores/config.txt
@@ -0,0 +1 @@
+--metric BIO-F1
diff --git a/test/bio-f1-simple-underscores/bio-f1-simple-underscores/test-A/expected.tsv b/test/bio-f1-simple-underscores/bio-f1-simple-underscores/test-A/expected.tsv
new file mode 100644
index 0000000..31de6dc
--- /dev/null
+++ b/test/bio-f1-simple-underscores/bio-f1-simple-underscores/test-A/expected.tsv
@@ -0,0 +1,3 @@
+O O B_city/POZNAŃ O O B_date/MARCH I_date/12
+O O O O
+O B_city/KONIN O