diff --git a/CMakeLists.txt b/CMakeLists.txt
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -109,6 +109,7 @@
     -DQT_NO_URL_CAST_FROM_STRING
     -DQT_STRICT_ITERATORS
     -DQT_USE_QSTRINGBUILDER
+    -DQT_NO_NARROWING_CONVERSIONS_IN_CONNECT
 )
 
 function(add_compile_flag_if_supported _flag)
diff --git a/kdevplatform/CMakeLists.txt b/kdevplatform/CMakeLists.txt
--- a/kdevplatform/CMakeLists.txt
+++ b/kdevplatform/CMakeLists.txt
@@ -56,6 +56,12 @@
   set(COMPILER_OPTIMIZATIONS_DISABLED FALSE)
 endif()
 
+add_definitions(
+    -DQT_NO_CAST_FROM_ASCII
+    -DQT_NO_CAST_TO_ASCII
+    -DQT_NO_CAST_FROM_BYTEARRAY
+)
+
 add_subdirectory(sublime)
 add_subdirectory(interfaces)
 add_subdirectory(project)
diff --git a/kdevplatform/language/CMakeLists.txt b/kdevplatform/language/CMakeLists.txt
--- a/kdevplatform/language/CMakeLists.txt
+++ b/kdevplatform/language/CMakeLists.txt
@@ -6,6 +6,11 @@
 check_include_file("malloc.h" HAVE_MALLOC_H)
 check_symbol_exists(malloc_trim "malloc.h" HAVE_MALLOC_TRIM)
 
+# TODO: fix duchain/stringhelpers.cpp and drop this again
+remove_definitions(
+    -DQT_NO_CAST_FROM_ASCII
+)
+
 if(BUILD_TESTING)
     add_subdirectory(highlighting/tests)
     add_subdirectory(duchain/tests)
diff --git a/kdevplatform/outputview/tests/CMakeLists.txt b/kdevplatform/outputview/tests/CMakeLists.txt
--- a/kdevplatform/outputview/tests/CMakeLists.txt
+++ b/kdevplatform/outputview/tests/CMakeLists.txt
@@ -1,3 +1,9 @@
+remove_definitions(
+    -DQT_NO_CAST_FROM_ASCII
+    -DQT_NO_CAST_TO_ASCII
+    -DQT_NO_CAST_FROM_BYTEARRAY
+)
+
 ecm_add_test(test_outputmodel LINK_LIBRARIES
     Qt5::Test
     KDev::Tests
diff --git a/kdevplatform/project/tests/CMakeLists.txt b/kdevplatform/project/tests/CMakeLists.txt
--- a/kdevplatform/project/tests/CMakeLists.txt
+++ b/kdevplatform/project/tests/CMakeLists.txt
@@ -1,3 +1,9 @@
+remove_definitions(
+    -DQT_NO_CAST_FROM_ASCII
+    -DQT_NO_CAST_TO_ASCII
+    -DQT_NO_CAST_FROM_BYTEARRAY
+)
+
 ecm_add_test(test_projectmodel.cpp
     LINK_LIBRARIES Qt5::Test KDev::Interfaces KDev::Project KDev::Language KDev::Tests)
 
diff --git a/kdevplatform/serialization/tests/CMakeLists.txt b/kdevplatform/serialization/tests/CMakeLists.txt
--- a/kdevplatform/serialization/tests/CMakeLists.txt
+++ b/kdevplatform/serialization/tests/CMakeLists.txt
@@ -1,5 +1,11 @@
 include_directories(${CMAKE_CURRENT_BINARY_DIR} ${CMAKE_CURRENT_SOURCE_DIR})
 
+remove_definitions(
+    -DQT_NO_CAST_FROM_ASCII
+    -DQT_NO_CAST_TO_ASCII
+    -DQT_NO_CAST_FROM_BYTEARRAY
+)
+
 if(NOT COMPILER_OPTIMIZATIONS_DISABLED)
     ecm_add_test(bench_itemrepository.cpp LINK_LIBRARIES
         LINK_LIBRARIES Qt5::Test KDev::Serialization KDev::Tests)
diff --git a/kdevplatform/shell/tests/CMakeLists.txt b/kdevplatform/shell/tests/CMakeLists.txt
--- a/kdevplatform/shell/tests/CMakeLists.txt
+++ b/kdevplatform/shell/tests/CMakeLists.txt
@@ -1,3 +1,9 @@
+remove_definitions(
+    -DQT_NO_CAST_FROM_ASCII
+    -DQT_NO_CAST_TO_ASCII
+    -DQT_NO_CAST_FROM_BYTEARRAY
+)
+
 ecm_add_test(test_documentcontroller.cpp
     LINK_LIBRARIES Qt5::Test KDev::Tests)
 
diff --git a/kdevplatform/sublime/tests/CMakeLists.txt b/kdevplatform/sublime/tests/CMakeLists.txt
--- a/kdevplatform/sublime/tests/CMakeLists.txt
+++ b/kdevplatform/sublime/tests/CMakeLists.txt
@@ -1,3 +1,9 @@
+remove_definitions(
+    -DQT_NO_CAST_FROM_ASCII
+    -DQT_NO_CAST_TO_ASCII
+    -DQT_NO_CAST_FROM_BYTEARRAY
+)
+
 set(test_areaoperation_SRCS test_areaoperation.cpp areaprinter.cpp)
 ecm_add_test(${test_areaoperation_SRCS}
     TEST_NAME test_areaoperation
diff --git a/kdevplatform/util/tests/CMakeLists.txt b/kdevplatform/util/tests/CMakeLists.txt
--- a/kdevplatform/util/tests/CMakeLists.txt
+++ b/kdevplatform/util/tests/CMakeLists.txt
@@ -1,3 +1,9 @@
+remove_definitions(
+    -DQT_NO_CAST_FROM_ASCII
+    -DQT_NO_CAST_TO_ASCII
+    -DQT_NO_CAST_FROM_BYTEARRAY
+)
+
 ecm_add_test(test_embeddedfreetree.cpp
     LINK_LIBRARIES KF5::TextEditor Qt5::Test KDev::Language KDev::Tests)
 
diff --git a/kdevplatform/vcs/models/tests/CMakeLists.txt b/kdevplatform/vcs/models/tests/CMakeLists.txt
--- a/kdevplatform/vcs/models/tests/CMakeLists.txt
+++ b/kdevplatform/vcs/models/tests/CMakeLists.txt
@@ -1,3 +1,9 @@
+remove_definitions(
+    -DQT_NO_CAST_FROM_ASCII
+    -DQT_NO_CAST_TO_ASCII
+    -DQT_NO_CAST_FROM_BYTEARRAY
+)
+
 ecm_add_test(test_models.cpp
     LINK_LIBRARIES Qt5::Test Qt5::Gui KDev::Tests KDev::Util KDev::Vcs
     GUI)
diff --git a/kdevplatform/vcs/tests/CMakeLists.txt b/kdevplatform/vcs/tests/CMakeLists.txt
--- a/kdevplatform/vcs/tests/CMakeLists.txt
+++ b/kdevplatform/vcs/tests/CMakeLists.txt
@@ -1,3 +1,9 @@
+remove_definitions(
+    -DQT_NO_CAST_FROM_ASCII
+    -DQT_NO_CAST_TO_ASCII
+    -DQT_NO_CAST_FROM_BYTEARRAY
+)
+
 ecm_add_test(test_vcsrevision
     LINK_LIBRARIES Qt5::Test KDev::Vcs
 )