diff --git a/io1_add_target.cmake b/io1_add_target.cmake
index bf573a0..6b2fc71 100644
--- a/io1_add_target.cmake
+++ b/io1_add_target.cmake
@@ -227,34 +227,16 @@ function(fetch_source_files out_sources)
       PARENT_SCOPE)
 endfunction()
 
-
-function(apply_source_files_properties)
-  foreach(str IN LISTS ARGN)
-    is_source_group("${str}" out)
-    if(out)
-      continue()
-    endif()
-
-    parse_file_options("${str}" file options)
-
-    cmake_parse_arguments(io1 "cpp;header" "" "" ${options})
-    if(io1_cpp)
-      set_source_files_properties("${file}" PROPERTIES LANGUAGE CXX)
-    endif()
-    if(io1_header)
-      set_source_files_properties("${file}" PROPERTIES HEADER_FILE_ONLY ON)
-    endif()
-  endforeach()
-endfunction()
-
-# adds src to target, applying options
-function(io1_add_source_file target file props)
+# adds src to target, applying options and source group
+function(io1_add_source_file target file props group)
 	get_target_property(type ${target} TYPE)
 	if (${type} STREQUAL "INTERFACE_LIBRARY")
 		target_sources(${target} INTERFACE ${file})
 	else()
 		target_sources(${target} PRIVATE ${file})
 	endif()
+	
+	source_group(NAME "${group}" FILES "${file}")
 
 	cmake_parse_arguments(io1 "cpp;header" "" "" ${props})
 	if(io1_header)
@@ -275,34 +257,24 @@ function(io1_is_source_group str res)
 endfunction()
 
 # expects "file.c[:opt1,opt2,opt3,...]" and parse it into "file.c" and the list
-# "opt1;opt2;opt3"
+# "opt1 opt2 opt3"
 function(io1_parse_file_options str out_file out_options)
 	if("${str}" MATCHES "^(.*):(.*)$")
 		if ("${CMAKE_MATCH_1}" STREQUAL "")
 			message(FATAL_ERROR "${CMAKE_CURRENT_FUNCTION}: ignored orphaned source option '${CMAKE_MATCH_2}'.")
 		else()
-			set(${out_file}
-				"${CMAKE_MATCH_1}"
-				PARENT_SCOPE)
+			set(${out_file}	"${CMAKE_MATCH_1}" PARENT_SCOPE)
 
 			if("${CMAKE_MATCH_2}" STREQUAL "")
-				unset(${out_options}
-				PARENT_SCOPE)
+				unset(${out_options} PARENT_SCOPE)
 			else()
 				string(REPLACE "," ";" temp_out_options "${CMAKE_MATCH_2}")
-				set(${out_options}
-					"${temp_out_options}"
-					PARENT_SCOPE)
+				set(${out_options} "${temp_out_options}" PARENT_SCOPE)
 			endif()
 		endif()
 	else()
-		set(${out_file}
-			"${str}"
-			PARENT_SCOPE
-		)
-		unset(${out_options}
-			PARENT_SCOPE
-		)
+		set(${out_file} "${str}" PARENT_SCOPE)
+		unset(${out_options} PARENT_SCOPE)
 	endif()
 endfunction()
 
diff --git a/test/add_source_file.cmake b/test/add_source_file.cmake
index 76899a6..0db2150 100644
--- a/test/add_source_file.cmake
+++ b/test/add_source_file.cmake
@@ -6,7 +6,7 @@ function(${CMAKETEST_TEST})
 
 	project(foo LANGUAGES CXX)
 	add_library(foo STATIC)
-	io1_add_source_file(foo "foo/main.cpp" "")
+	io1_add_source_file(foo "foo/main.cpp" "" "")
 	
 	get_target_property(prop foo SOURCES)
 	ct_assert_equal(prop "foo/main.cpp") # main.cpp was added to sources
@@ -25,7 +25,7 @@ function(${CMAKETEST_TEST})
 	
 	project(foo_header LANGUAGES CXX)
 	add_library(foo_header STATIC "foo_header/main.cpp")
-	io1_add_source_file(foo_header "foo_header/header.cpp" "header")
+	io1_add_source_file(foo_header "foo_header/header.cpp" "header" "")
 
 	get_target_property(prop foo_header SOURCES)
 	ct_assert_equal(prop "foo_header/main.cpp;foo_header/header.cpp") # header.cpp was added to sources
@@ -43,7 +43,7 @@ function(${CMAKETEST_TEST})
 
 	project(foo_cpp LANGUAGES CXX)
 	add_library(foo_cpp STATIC)
-	io1_add_source_file(foo_cpp "foo_cpp/main.c" "cpp")
+	io1_add_source_file(foo_cpp "foo_cpp/main.c" "cpp" "")
 
 	get_target_property(prop foo_cpp SOURCES)
 	ct_assert_equal(prop "foo_cpp/main.c") # main.c was added to sources
@@ -62,7 +62,7 @@ function(${CMAKETEST_TEST})
 
 	project(foo_cpp_header LANGUAGES CXX)
 	add_library(foo_cpp_header STATIC foo_cpp_header/main.cpp)
-	io1_add_source_file(foo_cpp_header "foo_cpp_header/header.c" "cpp;header")
+	io1_add_source_file(foo_cpp_header "foo_cpp_header/header.c" "cpp;header" "")
 
 	get_target_property(prop foo_cpp_header SOURCES)
 	ct_assert_equal(prop "foo_cpp_header/main.cpp;foo_cpp_header/header.c") # header.c was added to sources
@@ -81,7 +81,7 @@ function(${CMAKETEST_TEST})
 
 	project(foo_header_cpp LANGUAGES CXX)
 	add_library(foo_header_cpp STATIC foo_header_cpp/main.cpp)
-	io1_add_source_file(foo_header_cpp "foo_header_cpp/header.c" "header;cpp")
+	io1_add_source_file(foo_header_cpp "foo_header_cpp/header.c" "header;cpp" "")
 
 	get_target_property(prop foo_header_cpp SOURCES)
 	ct_assert_equal(prop "foo_header_cpp/main.cpp;foo_header_cpp/header.c") # header.c was added to sources