diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 06a90ad..7e31e93 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -7,10 +7,14 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
+    - name: Tools
+      run: sudo apt-get -y install tree
     - name: Configure
       run: cmake -DSANITIZE_ADDRESS=On .
     - name: Build
-      run: cmake --build .
+      run: |
+        cmake --build .
+        tree -sha .
     - name: Test
       run: ASAN_OPTIONS=detect_leaks=0 LSAN_OPTIONS=verbosity=1:log_threads=1 ctest -VV
 
@@ -18,12 +22,16 @@ jobs:
     runs-on: macos-latest
     steps:
     - uses: actions/checkout@v2
+    - name: Tools
+      run: brew install tree
     - name: Configure
       run: |
         pip3 install scan-build
         scan-build cmake -DSANITIZE_ADDRESS=On .
     - name: Build
-      run: scan-build -v --exclude test -enable-checker security.FloatLoopCounter -enable-checker security.insecureAPI.UncheckedReturn --status-bugs cmake --build .
+      run: |
+        scan-build -v --exclude test -enable-checker security.FloatLoopCounter -enable-checker security.insecureAPI.UncheckedReturn --status-bugs cmake --build .
+        tree -sha .
     - name: Test
       run:  ctest -VV
 
@@ -33,8 +41,10 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: Configure
-      run:  cmake  .
+      run:  cmake -DCMAKE_WINDOWS_EXPORT_ALL_SYMBOLS=TRUE .
     - name: Build
-      run:  cmake --build . --config "Debug"
+      run: |
+        cmake --build . --config "Debug"
+        tree /a /f .
     - name: Test
-      run:  ctest -VV -C "Debug"
+      run: ctest -VV -C "Debug"
diff --git a/CMakeLists.txt b/CMakeLists.txt
index f194649..dc42aa9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.0)
+cmake_minimum_required(VERSION 3.4)
 
 project(zip
   LANGUAGES C
@@ -20,7 +20,21 @@ endif (MSVC)
 
 # zip
 set(SRC src/miniz.h src/zip.h src/zip.c)
-add_library(${PROJECT_NAME} ${SRC})
+
+# this is the "object library" target: compiles the sources only once
+add_library(OBJLIB OBJECT ${SRC})
+# shared libraries need PIC
+set_property(TARGET OBJLIB PROPERTY POSITION_INDEPENDENT_CODE 1)
+
+# static and shared libraries built from the same object files
+if (BUILD_SHARED_LIBS)
+  add_library(${PROJECT_NAME} SHARED $<TARGET_OBJECTS:OBJLIB>)
+  include(GenerateExportHeader)
+  generate_export_header(${PROJECT_NAME})
+else()
+  add_library(${PROJECT_NAME} STATIC $<TARGET_OBJECTS:OBJLIB>)
+endif()
+
 target_include_directories(${PROJECT_NAME} PUBLIC
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>
   $<INSTALL_INTERFACE:include>
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 1224115..04c2123 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 2.8)
+cmake_minimum_required(VERSION 3.4)
 
 # test
 set(test_out test.out)