diff --git a/gcc/m2/gm2-compiler/P0SyntaxCheck.bnf b/gcc/m2/gm2-compiler/P0SyntaxCheck.bnf
index 868484c9b622..4e468bdae571 100644
--- a/gcc/m2/gm2-compiler/P0SyntaxCheck.bnf
+++ b/gcc/m2/gm2-compiler/P0SyntaxCheck.bnf
@@ -968,7 +968,7 @@ NamedOperand := '[' Ident ']' =:
 
 AsmOperandName := [ NamedOperand ] =:
 
-AsmOperands  := ConstExpression ':' AsmList [ ':' AsmList [ ':' TrashList ] ]
+AsmOperands  := ConstExpression [ ':' AsmList [ ':' AsmList [ ':' TrashList ] ] ]
               =:
 
 AsmList      := [ AsmElement ] { ',' AsmElement } =:
diff --git a/gcc/m2/gm2-compiler/P1Build.bnf b/gcc/m2/gm2-compiler/P1Build.bnf
index ac96ddb383f1..42d034dffe7e 100644
--- a/gcc/m2/gm2-compiler/P1Build.bnf
+++ b/gcc/m2/gm2-compiler/P1Build.bnf
@@ -1048,7 +1048,7 @@ NamedOperand := '[' Ident ']' =:
 
 AsmOperandName := [ NamedOperand ] =:
 
-AsmOperands  := ConstExpression ':' AsmList [ ':' AsmList [ ':' TrashList ] ]
+AsmOperands  := ConstExpression [ ':' AsmList [ ':' AsmList [ ':' TrashList ] ] ]
               =:
 
 AsmList      := [ AsmElement ] { ',' AsmElement } =:
diff --git a/gcc/m2/gm2-compiler/P2Build.bnf b/gcc/m2/gm2-compiler/P2Build.bnf
index e3db5f077dc6..86fbe1565f10 100644
--- a/gcc/m2/gm2-compiler/P2Build.bnf
+++ b/gcc/m2/gm2-compiler/P2Build.bnf
@@ -1257,7 +1257,7 @@ NamedOperand := '[' Ident ']' =:
 
 AsmOperandName := [ NamedOperand ] =:
 
-AsmOperands  := ConstExpression ':' AsmList [ ':' AsmList [ ':' TrashList ] ]
+AsmOperands  := ConstExpression [ ':' AsmList [ ':' AsmList [ ':' TrashList ] ] ]
               =:
 
 AsmList      := [ AsmElement ] { ',' AsmElement } =:
diff --git a/gcc/m2/gm2-compiler/PCBuild.bnf b/gcc/m2/gm2-compiler/PCBuild.bnf
index 263ac9b40316..2731e8940e6a 100644
--- a/gcc/m2/gm2-compiler/PCBuild.bnf
+++ b/gcc/m2/gm2-compiler/PCBuild.bnf
@@ -1292,7 +1292,7 @@ NamedOperand := '[' Ident ']' =:
 
 AsmOperandName := [ NamedOperand ] =:
 
-AsmOperands  := ConstExpression ':' AsmList [ ':' AsmList [ ':' TrashList ] ]
+AsmOperands  := ConstExpression [ ':' AsmList [ ':' AsmList [ ':' TrashList ] ] ]
               =:
 
 AsmList      := [ AsmElement ] { ',' AsmElement } =:
diff --git a/gcc/m2/gm2-compiler/PHBuild.bnf b/gcc/m2/gm2-compiler/PHBuild.bnf
index 55f4e9008f31..589385277768 100644
--- a/gcc/m2/gm2-compiler/PHBuild.bnf
+++ b/gcc/m2/gm2-compiler/PHBuild.bnf
@@ -1246,7 +1246,7 @@ NamedOperand := '[' Ident ']' =:
 
 AsmOperandName := [ NamedOperand ] =:
 
-AsmOperands  := ConstExpression ':' AsmList [ ':' AsmList [ ':' TrashList ] ]
+AsmOperands  := ConstExpression [ ':' AsmList [ ':' AsmList [ ':' TrashList ] ] ]
               =:
 
 AsmList      := [ AsmElement ] { ',' AsmElement } =:
diff --git a/gcc/testsuite/gm2/extensions/asm/pass/conststr.mod b/gcc/testsuite/gm2/extensions/asm/pass/conststr.mod
new file mode 100644
index 000000000000..bbe69394f0ea
--- /dev/null
+++ b/gcc/testsuite/gm2/extensions/asm/pass/conststr.mod
@@ -0,0 +1,5 @@
+MODULE conststr ;
+
+BEGIN
+   ASM VOLATILE ("")
+END conststr.