diff --git a/src/hoaparse/hoaparse.yy b/src/hoaparse/hoaparse.yy
index 3c9181a6b..4ae1eb40c 100644
--- a/src/hoaparse/hoaparse.yy
+++ b/src/hoaparse/hoaparse.yy
@@ -549,7 +549,7 @@ trans-label: label
 	         {
 		   if (res.has_state_label)
 		     {
-		       error(@1, "cannot label this transition because...");
+		       error(@1, "cannot label this edge because...");
 		       error(res.state_label_loc,
 			     "... the state is already labeled.");
 		       res.cur_label = res.state_label;
@@ -586,11 +586,30 @@ acc-sets:
 	    else
 	      $$ = $1 | res.h->aut->acc().mark($2);
 	  }
-labeled-edges: | labeled-edges labeled-edge
+
+/* block of labeled-edges, with occasional (incorrect) unlabeled edge */
+labeled-edges: | some-labeled-edges
+some-labeled-edges: labeled-edge
+                  | some-labeled-edges labeled-edge
+                  | some-labeled-edges incorrectly-unlabeled-edge
+incorrectly-unlabeled-edge: checked-state-num acc-sig_opt
+                            {
+			      bdd cond = bddtrue;
+			      if (!res.has_state_label)
+				error(@$, "missing label for this edge "
+				      "(previous edge is labeled)");
+			      else
+				cond = res.state_label;
+			      res.h->aut->new_transition(res.cur_state, $1,
+							 cond,
+							 $2 | res.acc_state);
+			    }
 labeled-edge: trans-label checked-state-num acc-sig_opt
 	      {
-		res.h->aut->new_transition(res.cur_state, $2,
-					   res.cur_label, $3 | res.acc_state);
+		if (res.cur_label != bddfalse)
+		  res.h->aut->new_transition(res.cur_state, $2,
+					     res.cur_label,
+					     $3 | res.acc_state);
 	      }
 	    | trans-label state-conj-2 acc-sig_opt
 	      {
@@ -598,9 +617,12 @@ labeled-edge: trans-label checked-state-num acc-sig_opt
 		YYABORT;
 	      }
 
-/* We never have zero unlabeled edges, these are considered as zero
-   labeled edges. */
-unlabeled-edges: unlabeled-edge | unlabeled-edges unlabeled-edge
+/* Block of unlabeled edge, with occasional (incorrect) labeled
+   edge. We never have zero unlabeled edges, these are considered as
+   zero labeled edges. */
+unlabeled-edges: unlabeled-edge
+               | unlabeled-edges unlabeled-edge
+               | unlabeled-edges incorrectly-labeled-edge
 unlabeled-edge: checked-state-num acc-sig_opt
 		{
 		  bdd cond;
@@ -623,14 +645,20 @@ unlabeled-edge: checked-state-num acc-sig_opt
 			  cond = *res.cur_guard++;
 			}
 		    }
-		  res.h->aut->new_transition(res.cur_state, $1,
-					     cond, $2 | res.acc_state);
+		  if (cond != bddfalse)
+		    res.h->aut->new_transition(res.cur_state, $1,
+					       cond, $2 | res.acc_state);
 		}
 	      | state-conj-2 acc-sig_opt
 		{
 		  error(@1, "alternation is not yet supported");
 		  YYABORT;
 		}
+incorrectly-labeled-edge: trans-label unlabeled-edge
+                          {
+			    error(@1, "ignoring this label, because previous"
+				  " edge has no label");
+                          }
 
 %%
 
diff --git a/src/hoaparse/hoascan.ll b/src/hoaparse/hoascan.ll
index cb751b183..7df03ae9c 100644
--- a/src/hoaparse/hoascan.ll
+++ b/src/hoaparse/hoascan.ll
@@ -30,6 +30,8 @@
 #define YY_NEVER_INTERACTIVE 1
 
 typedef hoayy::parser::token token;
+static unsigned comment_level = 0;
+
 %}
 
 eol         \n+|\r+
@@ -50,8 +52,7 @@ identifier  [[:alpha:]_][[:alnum:]_-]*
 {eol}			yylloc->lines(yyleng); yylloc->step();
 {eol2}			yylloc->lines(yyleng / 2); yylloc->step();
 [ \t\v\f]+		yylloc->step();
-"/*"			BEGIN(in_COMMENT);
-"//".*			continue;
+"/""*"+			BEGIN(in_COMMENT); comment_level = 1;
 "\""			BEGIN(in_STRING);
 
 "HOA:"                  return token::HOA;
@@ -97,10 +98,12 @@ identifier  [[:alpha:]_][[:alnum:]_-]*
 			}
 
 <in_COMMENT>{
-  [^*\n]*		continue;
+  "/""*"+		++comment_level;
+  [^*/\n]*		continue;
+  "/"[^*\n]*		continue;
   "*"+[^*/\n]*		continue;
   "\n"+			yylloc->end.column = 1;	yylloc->lines(yyleng);
-  "*"+"/"		BEGIN(INITIAL);
+  "*"+"/"		if (--comment_level == 0) BEGIN(INITIAL);
   <<EOF>>		{
                            error_list.push_back(
 			     spot::hoa_parse_error(*yylloc,
@@ -155,6 +158,7 @@ namespace spot
     // ended badly.
     YY_NEW_FILE;
     BEGIN(INITIAL);
+    comment_level = 0;
     return 0;
   }
 
diff --git a/src/tgbatest/hoaparse.test b/src/tgbatest/hoaparse.test
index b28d18362..a7258ac4d 100755
--- a/src/tgbatest/hoaparse.test
+++ b/src/tgbatest/hoaparse.test
@@ -300,6 +300,7 @@ EOF
 
 cat >input<<EOF
     HOA: v1
+    tool: "test"
     States: 3
     Start: 0
     acc-name: generalized-Buchi 2
@@ -320,7 +321,7 @@ cat >input<<EOF
 EOF
 
 expecterr input <<EOF
-input:13.7: too many transition for this state, ignoring this one
+input:14.7: too many transition for this state, ignoring this one
 EOF
 
 
@@ -356,7 +357,7 @@ cat >input <<EOF
     name: "GFa & GF(b & c)"
     States: 1
     Start: 0
-    acc-name: generalized-Buchi 2
+    acc-name: who cares
     Acceptance: 2 (Inf(0) & Inf(1))
     AP: 3 "a" "b" "c"
     Alias: @a 0
@@ -417,6 +418,7 @@ State: 0 {0}
 State: 1
 [!0] 1
 [0] 0
+[f] 0
 --END--
 EOF
 
@@ -499,7 +501,7 @@ Acceptance: 1 Inf(0)
 --BODY--
 State: 0 {0}
 [1] 1
-[!1] 0
+[!1] 0  /* nested /* comment */ */
 State: 1
 [!0] 1
 [0] 0
@@ -524,6 +526,33 @@ State: 1
 --END--
 EOF
 
+cat >input <<EOF
+HOA: v1
+States: 3
+Start: 0
+AP: 2 "a" "b"
+Acceptance: 1 Inf(0)
+--BODY--
+State: [1] 0 {0}
+[!1] 0
+ 1
+State: 1
+[!0] 1
+     2
+State: 2
+     1
+[t] 2
+   1 2
+--END--
+EOF
+
+expecterr input <<EOF
+input:8.1-4: cannot label this edge because...
+input:7.8-10: ... the state is already labeled.
+input:12.6: missing label for this edge (previous edge is labeled)
+input:15.1-3: ignoring this label, because previous edge has no label
+EOF
+
 
 cat >input <<EOF
 HOA: v1
@@ -618,3 +647,73 @@ input:32.1-5: syntax error, unexpected header name, expecting --END-- or State:
 input:37.1-4: syntax error, unexpected identifier, expecting end of file or HOA:
 input:39.1-3: syntax error, unexpected identifier, expecting end of file or HOA:
 EOF
+
+# A comment can contain --BODY-- or --END--, so we do not want to be
+# smart about it.
+cat >input <<EOF
+HOA: v1
+States: 2
+Start: 0
+AP: 0
+acc-name: Buchi /* unclosed comment
+Acceptance: 1 Inf(0)
+--BODY--
+State: 0 {0}
+[t] 1
+State: 1
+[t] 0
+--END--
+HOA: v1
+States: 2
+Start: 0
+AP: 0
+acc-name: Buchi
+Acceptance: 1 Inf(0)
+--BODY--
+State: 0 {0}
+[t] 1
+State: 1
+[t] 0
+--END--
+EOF
+
+expecterr input <<EOF
+input:5.17-25.1: unclosed comment
+input:5.17-25.1: syntax error, unexpected end of file
+autfilt: failed to read automaton from input
+EOF
+
+# Likewise for strings
+cat >input <<EOF
+HOA: v1
+States: 2
+Start: 0
+tool: "unterminated string
+AP: 0
+acc-name: Buchi
+Acceptance: 1 Inf(0)
+--BODY--
+State: 0 {0}
+[t] 1
+State: 1
+[t] 0
+--END--
+HOA: v1
+States: 2
+Start: 0
+AP: 0
+acc-name: Buchi
+Acceptance: 1 Inf(0)
+--BODY--
+State: 0 {0}
+[t] 1
+State: 1
+[t] 0
+--END--
+EOF
+
+expecterr input <<EOF
+input:4.7-242: unclosed string
+input:4.7-242: syntax error, unexpected end of file, expecting string
+autfilt: failed to read automaton from input
+EOF