diff --git a/CMakeLists.txt b/CMakeLists.txt
index dbec4dae..0ae80c74 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -19,10 +19,10 @@ add_definitions(-DZINT_VERSION=\"${ZINT_VERSION}\")
 
 set(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake/modules")
 
-set(ZINT_DEBUG FALSE CACHE BOOL "Set debug compile flag")
-set(ZINT_SANITIZE FALSE CACHE BOOL "Set sanitize compile/link flags")
-set(ZINT_TEST FALSE CACHE BOOL "Set test compile flag")
-set(ZINT_STATIC FALSE CACHE BOOL "Build static library")
+option(ZINT_DEBUG    "Set debug compile flag"          OFF)
+option(ZINT_SANITIZE "Set sanitize compile/link flags" OFF)
+option(ZINT_TEST     "Set test compile flag"           OFF)
+option(ZINT_STATIC   "Build static library"            OFF)
 
 include(SetPaths.cmake)
 
diff --git a/backend/png.c b/backend/png.c
index cf8a2377..0de9f20d 100644
--- a/backend/png.c
+++ b/backend/png.c
@@ -138,7 +138,7 @@ INTERNAL int png_pixel_plot(struct zint_symbol *symbol, unsigned char *pixelbuf)
         bg_alpha = 0xff;
     }
 
-    num_palette = num_trans = 0;
+    num_trans = 0;
     if (symbol->symbology == BARCODE_ULTRA) {
         static const int ultra_chars[8] = { 'W', 'C', 'B', 'M', 'R', 'Y', 'G', 'K' };
         static png_color ultra_colours[8] = {
diff --git a/backend/tests/CMakeLists.txt b/backend/tests/CMakeLists.txt
index 50178d28..e947de12 100644
--- a/backend/tests/CMakeLists.txt
+++ b/backend/tests/CMakeLists.txt
@@ -10,9 +10,9 @@ enable_testing()
 
 set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/cmake/Modules/")
 
-set(ZINT_DEBUG FALSE CACHE BOOL "Set debug compile flag")
-set(ZINT_SANITIZE FALSE CACHE BOOL "Set sanitize compile/link flags")
-set(ZINT_TEST FALSE CACHE BOOL "Set test compile flag")
+option(ZINT_DEBUG    "Set debug compile flag"          OFF)
+option(ZINT_SANITIZE "Set sanitize compile/link flags" OFF)
+option(ZINT_TEST     "Set test compile flag"           OFF)
 
 find_package(LibZint REQUIRED)
 find_package(PNG)
diff --git a/backend/tests/README b/backend/tests/README
index b348bbe1..3386e9ba 100644
--- a/backend/tests/README
+++ b/backend/tests/README
@@ -6,7 +6,7 @@ To make, first make libzint with ZINT_TEST defined:
   cd <project-dir>
   mkdir build
   cd build
-  cmake -DZINT_TEST:BOOL=1 ..
+  cmake -DZINT_TEST=ON ..
   make
 
 Then make the tests:
@@ -15,7 +15,7 @@ Then make the tests:
   cd backend/tests
   mkdir build
   cd build
-  cmake -DZINT_TEST:BOOL=1 ..
+  cmake -DZINT_TEST=ON ..
   make
 
 (ZINT_TEST is needed to export INTERNAL functions for use and testing.)
@@ -62,35 +62,35 @@ To make with gcc sanitize, first set for libzint and make:
 
   cd <project-dir>
   cd build
-  cmake -DZINT_SANITIZE:BOOL=1 ..
+  cmake -DZINT_SANITIZE=ON ..
   make && sudo make install
 
 Then set for tests and make:
 
   cd <project-dir>
   cd backend/tests/build
-  cmake -DZINT_SANITIZE:BOOL=1 ..
+  cmake -DZINT_SANITIZE=ON ..
   make
 
 Similarly to make with gcc debug:
 
   cd <project-dir>
   cd build
-  cmake -DZINT_DEBUG:BOOL=1 ..
+  cmake -DZINT_DEBUG=ON ..
   make && sudo make install
 
   cd <project-dir>
   cd backend/tests/build
-  cmake -DZINT_DEBUG:BOOL=1 ..
+  cmake -DZINT_DEBUG=ON ..
   make
 
 To undo sanitize/debug, remake each after setting:
 
-  cmake -DZINT_SANITIZE:BOOL=0 ..
-  cmake -DZINT_DEBUG:BOOL=0 ..
+  cmake -DZINT_SANITIZE=OFF ..
+  cmake -DZINT_DEBUG=OFF ..
 
 To get a clean libzint, set the above and also:
 
-  cmake -DZINT_TEST:BOOL=0 ..
+  cmake -DZINT_TEST=OFF ..
 
 (The tests will now fail to link.)