diff --git a/README.md b/README.md
index eee09f52..9a6d41c8 100644
--- a/README.md
+++ b/README.md
@@ -73,6 +73,18 @@ installation via an environment variable:
 set OPENSSL_DIR=C:\OpenSSL-Win64
 ```
 
+Note that this OpenSSL distribution does not ship with any root certificates.
+So to make requests to servers on the internet, you have to install them
+manually. Download the [cacert.pem file from here], copy it somewhere safe
+(`C:\OpenSSL-Win64\certs` is a good place) and point the `SSL_CERT_FILE`
+environment variable there:
+
+```
+set SSL_CERT_FILE=C:\OpenSSL-Win64\certs\cacert.pem
+```
+
+[cacert.pem file from here]: https://curl.haxx.se/docs/caextract.html
+
 After that, you're just a `cargo build` away!
 
 ### Windows GNU (MinGW)
@@ -102,6 +114,12 @@ The build script can be configured via environment variables:
 * `OPENSSL_DIR` - If specified, a directory that will be used to find
   OpenSSL installation. It's expected that under this directory the `include`
   folder has header files and a `lib` folder has the runtime libraries.
+* `OPENSSL_LIB_DIR` - If specified, a directory that will be used to find
+  OpenSSL libraries. Overrides the `lib` folder implied by `OPENSSL_DIR`
+  (if specified).
+* `OPENSSL_INCLUDE_DIR` - If specified, a directory that will be used to find
+  OpenSSL header files. Overrides the `include` folder implied by `OPENSSL_DIR`
+  (if specified).
 * `OPENSSL_STATIC` - If specified, OpenSSL libraries will be statically rather
   than dynamically linked.
 
diff --git a/openssl-sys/build.rs b/openssl-sys/build.rs
index b6c8c2de..ce173192 100644
--- a/openssl-sys/build.rs
+++ b/openssl-sys/build.rs
@@ -11,17 +11,25 @@ use std::process::Command;
 fn main() {
     let target = env::var("TARGET").unwrap();
 
-    let openssl_dir = env::var_os("OPENSSL_DIR").unwrap_or_else(|| {
-        find_openssl_dir(&target)
-    });
+    let lib_dir = env::var_os("OPENSSL_LIB_DIR").map(PathBuf::from);
+    let include_dir = env::var_os("OPENSSL_INCLUDE_DIR").map(PathBuf::from);
+
+    let (lib_dir, include_dir) = if lib_dir.is_none() || include_dir.is_none() {
+        let openssl_dir = env::var_os("OPENSSL_DIR").unwrap_or_else(|| {
+            find_openssl_dir(&target)
+        });
+        let openssl_dir = Path::new(&openssl_dir);
+        let lib_dir = lib_dir.unwrap_or_else(|| openssl_dir.join("lib"));
+        let include_dir = include_dir.unwrap_or_else(|| openssl_dir.join("include"));
+        (lib_dir, include_dir)
+    } else {
+        (lib_dir.unwrap(), include_dir.unwrap())
+    };
 
-    let lib_dir = Path::new(&openssl_dir).join("lib");
-    let include_dir = Path::new(&openssl_dir).join("include");
     if !Path::new(&lib_dir).exists() {
         panic!("OpenSSL library directory does not exist: {}",
                lib_dir.to_string_lossy());
     }
-
     if !Path::new(&include_dir).exists() {
         panic!("OpenSSL include directory does not exist: {}",
                include_dir.to_string_lossy());