diff --git a/CMakeLists.txt b/CMakeLists.txt
index 627f4d56..e32ad3a2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -390,12 +390,16 @@ endif()
 # Detect platform-specific crypto-backends last:
 
 if(CRYPTO_BACKEND STREQUAL "WinCNG" OR NOT CRYPTO_BACKEND)
-  set(CRYPTO_BACKEND "WinCNG")
-  set(CRYPTO_BACKEND_DEFINE "LIBSSH2_WINCNG")
-  set(CRYPTO_BACKEND_INCLUDE_DIR "")
+  if(WIN32)
+    set(CRYPTO_BACKEND "WinCNG")
+    set(CRYPTO_BACKEND_DEFINE "LIBSSH2_WINCNG")
+    set(CRYPTO_BACKEND_INCLUDE_DIR "")
 
-  list(APPEND LIBRARIES crypt32 bcrypt)
-  list(APPEND PC_LIBS -lcrypt32 -lbcrypt)
+    list(APPEND LIBRARIES crypt32 bcrypt)
+    list(APPEND PC_LIBS -lcrypt32 -lbcrypt)
+  elseif(${SPECIFIC_CRYPTO_REQUIREMENT} STREQUAL ${REQUIRED})
+    message(FATAL_ERROR "WinCNG not available")
+  endif()
 endif()
 
 # Global functions