diff --git a/regression_test/XML/Issue585/.gitignore b/regression_test/XML/Issue585/.gitignore
new file mode 100644
index 0000000000000000000000000000000000000000..a31edf8420c4386ed28be4787d8ab06e7d34019f
--- /dev/null
+++ b/regression_test/XML/Issue585/.gitignore
@@ -0,0 +1,7 @@
+Issue585
+Issue585.exe
+Issue585*.cc
+Issue585*.hh
+Issue585*.d
+compile
+Issue585*.log
diff --git a/regression_test/XML/Issue585/Issue585.ttcn b/regression_test/XML/Issue585/Issue585.ttcn
new file mode 100644
index 0000000000000000000000000000000000000000..d457deb2dcc3f51aa201002b736adac54c35cf11
--- /dev/null
+++ b/regression_test/XML/Issue585/Issue585.ttcn
@@ -0,0 +1,63 @@
+/******************************************************************************
+ * Copyright (c) 2000-2021 Ericsson Telecom AB
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/org/documents/epl-2.0/EPL-2.0.html
+ *
+ * Contributors:
+ *   Baranyi, Botond
+ *
+ ******************************************************************************/
+module Issue585 {
+
+type record Rec {
+  integer num,
+  Uni1 u1 optional,
+  Uni2 u2
+}
+
+type union Uni1 {
+  charstring x1,
+  octetstring x2
+}
+with {
+  variant "untagged";
+}
+
+type union Uni2 {
+  charstring y1,
+  octetstring y2
+}
+with {
+  variant "untagged";
+}
+
+type component CT {}
+
+testcase tc_issue585() runs on CT {
+  var Rec val := { 4, omit, { y2 := 'ABCD'O } };
+  var universal charstring enc := encvalue_unichar(val);
+  var universal charstring enc_exp := "<ns:Rec xmlns:ns='www.somewhere.com/xml2'>\n\t<ns:num>4</ns:num>\n\t<ns:y2>ABCD</ns:y2>\n</ns:Rec>\n\n";
+  if (enc != enc_exp) {
+    setverdict(fail, "Encoding failed. Expected: ", enc_exp, ", got: ", enc);
+  }
+  var Rec dec;
+  var integer res := decvalue_unichar(enc, dec);
+  if (res != 0 or dec != val) {
+    setverdict(fail, "Decoding failed. Expected: ", val, ", got: ", dec, " (result: ", res, ")");
+  }
+  setverdict(pass);
+}
+
+control {
+  execute(tc_issue585());
+}
+
+}
+with {
+  encode "XML";
+  variant "elementFormQualified";
+  variant "namespace as 'www.somewhere.com/xml2' prefix 'ns'";
+  variant "controlNamespace 'http://www.w3.org/2001/XMLSchema-instance' prefix 'xsi'";
+}
diff --git a/regression_test/XML/Issue585/Makefile b/regression_test/XML/Issue585/Makefile
new file mode 100644
index 0000000000000000000000000000000000000000..dc493ce710b334ebd75af1105cd67ec74f063980
--- /dev/null
+++ b/regression_test/XML/Issue585/Makefile
@@ -0,0 +1,147 @@
+##############################################################################
+# Copyright (c) 2000-2021 Ericsson Telecom AB
+# All rights reserved. This program and the accompanying materials
+# are made available under the terms of the Eclipse Public License v2.0
+# which accompanies this distribution, and is available at
+# https://www.eclipse.org/org/documents/epl-2.0/EPL-2.0.html
+#
+# Contributors:
+#   Baranyi, Botond
+#
+##############################################################################
+TOPDIR = ../..
+include $(TOPDIR)/Makefile.regression
+
+# WARNING! This Makefile can be used with GNU make only.
+# Other versions of make may report syntax errors in it.
+
+#
+# Do NOT touch this line...
+#
+.PHONY: all archive check clean dep objects
+
+.SUFFIXES: .d
+
+#
+# Set these variables...
+#
+
+# Flags for the C++ preprocessor (and makedepend as well):
+#CPPFLAGS +=
+
+# Flags for dependency generation
+CXXDEPFLAGS = -MM
+
+# Flags for the C++ compiler:
+CXXFLAGS += -Wall
+
+# Flags for the linker:
+#LDFLAGS += 
+
+# Flags for the TTCN-3 and ASN.1 compiler:
+#COMPILER_FLAGS +=  
+
+# Execution mode: (either ttcn3 or ttcn3-parallel)
+TTCN3_LIB = ttcn3$(RT2_SUFFIX)$(DYNAMIC_SUFFIX)
+
+#
+# You may change these variables. Add your files if necessary...
+#
+
+# TTCN-3 modules of this project:
+TTCN3_MODULES = Issue585.ttcn
+
+# ASN.1 modules of this project:
+ASN1_MODULES =
+
+# C++ source & header files generated from the TTCN-3 & ASN.1 modules of
+# this project:
+GENERATED_SOURCES = $(TTCN3_MODULES:.ttcn=.cc) $(ASN1_MODULES:.asn=.cc)
+GENERATED_HEADERS = $(GENERATED_SOURCES:.cc=.hh)
+ifdef SPLIT_TO_SLICES
+POSTFIXES := $(foreach file, $(SPLIT_TO_SLICES), $(addsuffix $(file), _part_))
+POSTFIXES := $(foreach file, $(POSTFIXES), $(addprefix $(file), .cc))
+GENERATED_SOURCES2 := $(foreach file, $(GENERATED_SOURCES:.cc=), $(addprefix $(file), $(POSTFIXES)))
+GENERATED_SOURCES += $(GENERATED_SOURCES2)
+endif
+# C/C++ Source & header files of Test Ports, external functions and
+# other modules:
+USER_SOURCES =
+USER_HEADERS = $(USER_SOURCES:.cc=.hh)
+
+# Object files of this project that are needed for the executable test suite:
+OBJECTS = $(GENERATED_OBJECTS) $(USER_OBJECTS)
+
+GENERATED_OBJECTS = $(GENERATED_SOURCES:.cc=.o)
+
+USER_OBJECTS = $(USER_SOURCES:.cc=.o)
+
+DEPFILES = $(USER_OBJECTS:.o=.d)  $(GENERATED_OBJECTS:.o=.d)
+
+# Other files of the project (Makefile, configuration files, etc.)
+# that will be added to the archived source files:
+OTHER_FILES = Makefile
+
+# The name of the executable test suite:
+TARGET = Issue585$(EXESUFFIX)
+
+#
+# Rules for building the executable...
+#
+
+all: $(TARGET) ;
+
+objects: $(OBJECTS) compile;
+
+$(TARGET): $(OBJECTS)
+	if $(CXX) $(LDFLAGS) -o $@ $^ \
+	-L$(TTCN3_DIR)/lib -l$(TTCN3_LIB) \
+	-L$(OPENSSL_DIR)/lib -lcrypto \
+	-L$(XMLDIR)/lib $($(PLATFORM)_LIBS); \
+	then : ; else $(TTCN3_DIR)/bin/titanver $(OBJECTS); exit 1; fi
+
+.cc.o .c.o:
+	$(CXX) -c $(CPPFLAGS) $(CXXFLAGS) -o $@ $<
+
+.cc.d .c.d:
+	@echo Creating dependency file for '$<'; set -e; \
+	$(CXX) $(CXXDEPFLAGS) $(CPPFLAGS) $(CXXFLAGS) $< \
+	| sed 's/\($*\)\.o[ :]*/\1.o $@ : /g' > $@; \
+	[ -s $@ ] || rm -f $@
+
+$(GENERATED_SOURCES) $(GENERATED_HEADERS): compile
+	@if [ ! -f $@ ]; then $(RM) compile; $(MAKE) compile; fi
+
+compile: $(TTCN3_MODULES) $(ASN1_MODULES)
+	$(TTCN3_COMPILER) $(COMPILER_FLAGS) $^ - $?
+	touch $@
+
+clean distclean:
+	-$(RM) $(TARGET) $(OBJECTS) $(GENERATED_HEADERS) \
+	$(GENERATED_SOURCES) compile $(DEPFILES) \
+	tags *.log
+
+dep: $(GENERATED_SOURCES) $(USER_SOURCES) ;
+
+ifeq ($(findstring n,$(MAKEFLAGS)),)
+ifeq ($(filter clean distclean check compile archive diag,$(MAKECMDGOALS)),)
+-include $(DEPFILES)
+endif
+endif
+
+diag:
+	$(TTCN3_COMPILER) -v 2>&1
+	$(TTCN3_DIR)/bin/mctr_cli -v 2>&1
+	$(CXX) -v 2>&1
+	@echo TTCN3_DIR=$(TTCN3_DIR)
+	@echo OPENSSL_DIR=$(OPENSSL_DIR)
+	@echo XMLDIR=$(XMLDIR)
+	@echo PLATFORM=$(PLATFORM)
+
+#
+# Add your rules here if necessary...
+#
+
+run: $(TARGET)
+	./$^
+