diff --git a/src/main/scala/smtlib/lexer/Lexer.scala b/src/main/scala/smtlib/lexer/Lexer.scala
index cff5677..f1d4f93 100644
--- a/src/main/scala/smtlib/lexer/Lexer.scala
+++ b/src/main/scala/smtlib/lexer/Lexer.scala
@@ -11,7 +11,7 @@ class Lexer(reader: java.io.Reader) {
   import Lexer._
 
   private def isNewLine(c: Char) = c == '\n' || c == '\r'
-  private def isBlank(c: Char) = c == '\n' || c == '\r' || c == ' '
+  private def isBlank(c: Char) = c == '\n' || c == '\r' || c == ' ' || c == '\t'
 
   /*
    * Note that we do not start reading the input until the next function is called.
diff --git a/src/test/scala/smtlib/parser/CommandsParserTests.scala b/src/test/scala/smtlib/parser/CommandsParserTests.scala
index bffbdc3..90034e9 100644
--- a/src/test/scala/smtlib/parser/CommandsParserTests.scala
+++ b/src/test/scala/smtlib/parser/CommandsParserTests.scala
@@ -98,6 +98,11 @@ class CommandsParserTests extends AnyFunSuite with TimeLimits {
 
 
   test("Parsing define-fun commands") {
+    assert(parseUniqueCmd("(define-fun $Perm.isValidVar ((p $Perm)) Bool\n\t(<= $Perm.No p))") ===
+      DefineFun(FunDef("$Perm.isValidVar", Seq(SortedVar("p", Sort("$Perm"))), Sort("Bool"), FunctionApplication(
+        QualifiedIdentifier("<="), Seq(QualifiedIdentifier("$Perm.No"), QualifiedIdentifier("p"))
+      )))
+    )
     assert(parseUniqueCmd("(define-fun f ((a A)) B a)") ===
            DefineFun(FunDef("f", Seq(SortedVar("a", Sort("A"))), Sort("B"), QualifiedIdentifier("a"))))
     assert(parseUniqueCmd("(define-fun f ((a A)) B (f a))") ===