diff --git a/src/osltoy/osltoyapp.cpp b/src/osltoy/osltoyapp.cpp
index 3e6a59d08..597768c07 100644
--- a/src/osltoy/osltoyapp.cpp
+++ b/src/osltoy/osltoyapp.cpp
@@ -711,6 +711,22 @@ OSLToyMainWindow::open_file(const std::string& filename)
 }
 
 
+void 
+OSLToyMainWindow::add_include_search_path(const std::string& path) 
+{
+    auto begin = m_include_search_paths.begin();
+    auto end = m_include_search_paths.end();
+    if (std::find(begin, end, path) == end) { 
+        m_include_search_paths.push_back(path);
+        m_should_regenerate_compile_options = true;
+
+        // Open question: Do we want to force a recompile whenever the list is updated?
+        //                For now this doesn't matter cause the list is only modified 
+        //                via command line arguments, but if we want to have a GUI component,
+        //                this is worth considering. 
+    }
+}
+
 
 void
 OSLToyMainWindow::action_saveas()
@@ -836,6 +852,24 @@ class MyOSLCErrorHandler final : public OIIO::ErrorHandler {
 };
 
 
+void 
+OSLToyMainWindow::regenerate_compile_options()
+{
+    // Right now, the only option we consider is include search path (-I)
+    
+    // Annoyingly, oslcomp only supports -I flags without any seperator between 
+    // the -I and the path itself, but OIIO::ArgParse does not support parsing
+    // arguments in this manner. Oy vey.
+
+    m_compile_options.clear();
+
+    for (auto&& path : m_include_search_paths) 
+        m_compile_options.push_back(std::string("-I").append(path));
+
+
+    m_should_regenerate_compile_options = false;
+}
+
 
 void
 OSLToyMainWindow::recompile_shaders()
@@ -863,11 +897,20 @@ OSLToyMainWindow::recompile_shaders()
             MyOSLCErrorHandler errhandler(this);
             OSLCompiler oslcomp(&errhandler);
             std::string osooutput;
-            std::vector<std::string> options;
-            ok = oslcomp.compile_buffer(source, osooutput, options, "",
+
+            if (m_should_regenerate_compile_options)
+                regenerate_compile_options();
+
+            ok = oslcomp.compile_buffer(source, osooutput, m_compile_options, "",
                                         briefname);
-            set_error_message(tab,
-                              OIIO::Strutil::join(errhandler.errors, "\n"));
+
+            auto error_message = OIIO::Strutil::fmt::format(
+                    "{}\n\nCompiled {} with options: {}", 
+                    OIIO::Strutil::join(errhandler.errors, "\n"),
+                    briefname, 
+                    OIIO::Strutil::join(m_compile_options, " "));
+            set_error_message(tab, error_message);
+            
             if (ok) {
                 // std::cout << osooutput << "\n";
                 ok = shadingsys()->LoadMemoryCompiledShader(briefname,
diff --git a/src/osltoy/osltoyapp.h b/src/osltoy/osltoyapp.h
index 3d4055ee8..aea7f8fe1 100644
--- a/src/osltoy/osltoyapp.h
+++ b/src/osltoy/osltoyapp.h
@@ -91,6 +91,8 @@ class OSLToyMainWindow final : public QMainWindow {
 
     bool open_file(const std::string& filename);
 
+    void add_include_search_path(const std::string& path);
+
     void rerender_needed() { m_rerender_needed = 1; }
 
 private slots:
@@ -183,6 +185,8 @@ private slots:
     void make_param_adjustment_row(ParamRec* param, QGridLayout* layout,
                                    int row);
 
+    void regenerate_compile_options();
+
     void rebuild_param_area();
     void inventory_params();
     OIIO::ImageBuf& framebuffer();
@@ -197,6 +201,13 @@ private slots:
     std::string m_groupname;
     bool m_shader_uses_time = false;
 
+    std::vector<std::string> m_include_search_paths;
+
+
+    bool m_should_regenerate_compile_options = true;
+    std::vector<std::string> m_compile_options;
+
+
     // Access control mutex for handing things off between the GUI thread
     // and the shading thread.
     OIIO::spin_mutex m_job_mutex;
diff --git a/src/osltoy/osltoymain.cpp b/src/osltoy/osltoymain.cpp
index 9b926e356..99b67f200 100644
--- a/src/osltoy/osltoymain.cpp
+++ b/src/osltoy/osltoymain.cpp
@@ -39,6 +39,7 @@ static bool foreground_mode = true;
 static int threads          = 0;
 static int xres = 512, yres = 512;
 static std::vector<std::string> filenames;
+static std::vector<std::string> include_paths;
 
 
 static void
@@ -58,6 +59,9 @@ getargs(int argc, char* argv[])
       .help("Set thread count (0=cores)");
     ap.arg("--res %d:XRES %d:YRES", &xres, &yres)
       .help("Set resolution");
+    ap.arg("-I DIRPATH")
+      .action([&](cspan<const char*> argv){ include_paths.emplace_back(argv[1]); })
+      .help("Add DIRPATH to the list of header search paths.");
     // clang-format on
     if (ap.parse(argc, (const char**)argv) < 0) {
         std::cerr << ap.geterror() << std::endl;
@@ -94,6 +98,10 @@ main(int argc, char* argv[])
     QApplication app(argc, argv);
     OSLToyMainWindow mainwin(rend, xres, yres);
     mainwin.show();
+
+    for (auto&& path : include_paths)
+        mainwin.add_include_search_path(path);
+
     for (auto&& filename : filenames)
         mainwin.open_file(filename);