src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/codegen/AssignSymbols.java

*** 341,351 ****
                  if (!isLocal(function, symbol)) {
                      // Not defined in this function. Create a new definition.
                      symbol = null;
                  } else if (symbol.isParam()) {
                      // Duplicate parameter. Null return will force an error.
!                     throw new AssertionError("duplicate parameter");
                  }
              } else if (isVar) {
                  if (isBlockScope) {
                      // Check redeclaration in same block
                      if (symbol.hasBeenDeclared()) {
--- 341,351 ----
                  if (!isLocal(function, symbol)) {
                      // Not defined in this function. Create a new definition.
                      symbol = null;
                  } else if (symbol.isParam()) {
                      // Duplicate parameter. Null return will force an error.
!                     throwParserException(ECMAErrors.getMessage("syntax.error.duplicate.parameter", name), origin);
                  }
              } else if (isVar) {
                  if (isBlockScope) {
                      // Check redeclaration in same block
                      if (symbol.hasBeenDeclared()) {