diff --git a/nac3core/build.rs b/nac3core/build.rs
index 0c9d6407..33cf3da9 100644
--- a/nac3core/build.rs
+++ b/nac3core/build.rs
@@ -46,6 +46,8 @@ fn compile_irrt_cpp() {
         "-Wall",
         "-Wextra",
         "-Werror=return-type",
+        "-I",
+        irrt_dir.to_str().unwrap(),
         "-o",
         "-",
         irrt_cpp_path.to_str().unwrap(),
@@ -133,6 +135,8 @@ fn compile_irrt_test_cpp() {
         "-Wextra",
         "-Werror=return-type",
         "-lm", // for `tgamma()`, `lgamma()`
+        "-I",
+        irrt_dir.to_str().unwrap(),
         "-o",
         exe_path.to_str().unwrap(),
     ];
diff --git a/nac3core/irrt/irrt.cpp b/nac3core/irrt/irrt.cpp
index 489ce090..f6e41655 100644
--- a/nac3core/irrt/irrt.cpp
+++ b/nac3core/irrt/irrt.cpp
@@ -1,5 +1,5 @@
 #define IRRT_DEFINE_TYPEDEF_INTS
-#include "irrt_everything.hpp"
+#include <irrt_everything.hpp>
 
 /*
     All IRRT implementations.
diff --git a/nac3core/irrt/irrt/core.hpp b/nac3core/irrt/irrt/core.hpp
index 31bec3fc..88a7e418 100644
--- a/nac3core/irrt/irrt/core.hpp
+++ b/nac3core/irrt/irrt/core.hpp
@@ -1,7 +1,7 @@
 #pragma once
 
-#include "utils.hpp"
-#include "int_defs.hpp"
+#include <irrt/utils.hpp>
+#include <irrt/int_defs.hpp>
 
 // NDArray indices are always `uint32_t`.
 using NDIndex = uint32_t;
diff --git a/nac3core/irrt/irrt/error_context.hpp b/nac3core/irrt/irrt/error_context.hpp
index 824f6eb7..2e656531 100644
--- a/nac3core/irrt/irrt/error_context.hpp
+++ b/nac3core/irrt/irrt/error_context.hpp
@@ -1,7 +1,7 @@
 #pragma once
 
-#include "int_defs.hpp"
-#include "utils.hpp"
+#include <irrt/int_defs.hpp>
+#include <irrt/utils.hpp>
 
 namespace {
 // nac3core's "str" struct type definition
diff --git a/nac3core/irrt/irrt/string_utils.hpp b/nac3core/irrt/irrt/string_utils.hpp
index c2750600..ec723dcb 100644
--- a/nac3core/irrt/irrt/string_utils.hpp
+++ b/nac3core/irrt/irrt/string_utils.hpp
@@ -1,6 +1,6 @@
 #pragma once
 
-#include "int_defs.hpp"
+#include <irrt/int_defs.hpp>
 
 namespace {
 namespace string {
diff --git a/nac3core/irrt/irrt/utils.hpp b/nac3core/irrt/irrt/utils.hpp
index 27dcbb6e..d7fa13eb 100644
--- a/nac3core/irrt/irrt/utils.hpp
+++ b/nac3core/irrt/irrt/utils.hpp
@@ -1,6 +1,6 @@
 #pragma once
 
-#include "int_defs.hpp"
+#include <irrt/int_defs.hpp>
 
 namespace {
 template <typename T>
diff --git a/nac3core/irrt/irrt_everything.hpp b/nac3core/irrt/irrt_everything.hpp
index 5abbf61f..e7919124 100644
--- a/nac3core/irrt/irrt_everything.hpp
+++ b/nac3core/irrt/irrt_everything.hpp
@@ -1,6 +1,6 @@
 #pragma once
 
-#include "irrt/core.hpp"
-#include "irrt/error_context.hpp"
-#include "irrt/int_defs.hpp"
-#include "irrt/utils.hpp"
\ No newline at end of file
+#include <irrt/core.hpp>
+#include <irrt/error_context.hpp>
+#include <irrt/int_defs.hpp>
+#include <irrt/utils.hpp>
\ No newline at end of file
diff --git a/nac3core/irrt/irrt_test.cpp b/nac3core/irrt/irrt_test.cpp
index 57cdd3e8..afc5be43 100644
--- a/nac3core/irrt/irrt_test.cpp
+++ b/nac3core/irrt/irrt_test.cpp
@@ -5,11 +5,11 @@
 #include <cstdio>
 #include <cstdlib>
 
-#include "irrt_everything.hpp"
+#include <irrt_everything.hpp>
 
-#include "test/core.hpp"
-#include "test/test_core.hpp"
-#include "test/test_utils.hpp"
+#include <test/core.hpp>
+#include <test/test_core.hpp>
+#include <test/test_utils.hpp>
 
 int main() {
     run_test_core();
diff --git a/nac3core/irrt/test/core.hpp b/nac3core/irrt/test/core.hpp
index 34063aa4..8726b766 100644
--- a/nac3core/irrt/test/core.hpp
+++ b/nac3core/irrt/test/core.hpp
@@ -6,7 +6,7 @@
 #include <cstdio>
 #include <cstdlib>
 
-#include "print.hpp"
+#include <test/print.hpp>
 
 // Some utils can be used here
 #include "../irrt/utils.hpp"
diff --git a/nac3core/irrt/test/test_core.hpp b/nac3core/irrt/test/test_core.hpp
index 1d5b7d93..94dd292d 100644
--- a/nac3core/irrt/test/test_core.hpp
+++ b/nac3core/irrt/test/test_core.hpp
@@ -1,7 +1,7 @@
 #pragma once
 
-#include "core.hpp"
-#include "../irrt/core.hpp"
+#include <test/core.hpp>
+#include <irrt/core.hpp>
 
 void test_int_exp() {
     BEGIN_TEST();
diff --git a/nac3core/irrt/test/test_utils.hpp b/nac3core/irrt/test/test_utils.hpp
index cad0da18..d8cc1f63 100644
--- a/nac3core/irrt/test/test_utils.hpp
+++ b/nac3core/irrt/test/test_utils.hpp
@@ -1,7 +1,7 @@
 #pragma once
 
-#include "core.hpp"
-#include "../irrt/utils.hpp"
+#include <test/core.hpp>
+#include <irrt/utils.hpp>
 
 void test_int_log_10() {
     BEGIN_TEST();