diff --git a/libs/geom/include/psemek/geom/box.hpp b/libs/geom/include/psemek/geom/box.hpp
index 799e8e9f..3c32d7b0 100644
--- a/libs/geom/include/psemek/geom/box.hpp
+++ b/libs/geom/include/psemek/geom/box.hpp
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <psemek/util/io_fwd.hpp>
+
 #include <psemek/geom/detail/array.hpp>
 #include <psemek/geom/interval.hpp>
 #include <psemek/geom/point.hpp>
@@ -239,8 +241,8 @@ namespace psemek::geom
 		return *this = *this | b;
 	}
 
-	template <typename Stream, typename T, std::size_t N>
-	Stream & operator << (Stream & os, box<T, N> const & b)
+	template <typename T, std::size_t N>
+	std::ostream & operator << (std::ostream & os, box<T, N> const & b)
 	{
 		for (std::size_t i = 0; i < N; ++i)
 		{
diff --git a/libs/geom/include/psemek/geom/interval.hpp b/libs/geom/include/psemek/geom/interval.hpp
index 0ccc0a63..dd3782c7 100644
--- a/libs/geom/include/psemek/geom/interval.hpp
+++ b/libs/geom/include/psemek/geom/interval.hpp
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <psemek/util/io_fwd.hpp>
+
 #include <limits>
 #include <type_traits>
 #include <cmath>
@@ -250,8 +252,8 @@ namespace psemek::geom
 		return i.min + i.length() * t;
 	}
 
-	template <typename Stream, typename T>
-	Stream & operator << (Stream & os, interval<T> const & i)
+	template <typename T>
+	std::ostream & operator << (std::ostream & os, interval<T> const & i)
 	{
 		os << '[' << i.min << " .. " << i.max << ']';
 		return os;
diff --git a/libs/geom/include/psemek/geom/matrix.hpp b/libs/geom/include/psemek/geom/matrix.hpp
index 556fe2df..41cec26e 100644
--- a/libs/geom/include/psemek/geom/matrix.hpp
+++ b/libs/geom/include/psemek/geom/matrix.hpp
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <psemek/util/io_fwd.hpp>
+
 #include <psemek/geom/detail/array.hpp>
 #include <psemek/geom/vector.hpp>
 #include <psemek/geom/math.hpp>
@@ -303,8 +305,8 @@ namespace psemek::geom
 		return r;
 	}
 
-	template <typename Stream, typename T, std::size_t R, std::size_t C>
-	Stream & operator << (Stream & os, matrix<T, R, C> const & m)
+	template <typename T, std::size_t R, std::size_t C>
+	std::ostream & operator << (std::ostream & os, matrix<T, R, C> const & m)
 	{
 		for (std::size_t i = 0; i < R; ++i)
 		{
diff --git a/libs/geom/include/psemek/geom/point.hpp b/libs/geom/include/psemek/geom/point.hpp
index 7f615c4c..202bf716 100644
--- a/libs/geom/include/psemek/geom/point.hpp
+++ b/libs/geom/include/psemek/geom/point.hpp
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <psemek/util/io_fwd.hpp>
+
 #include <psemek/geom/detail/array.hpp>
 #include <psemek/geom/vector.hpp>
 
@@ -188,8 +190,8 @@ namespace psemek::geom
 		return normalized(ort((ps - p0)...));
 	}
 
-	template <typename Stream, typename T, std::size_t N>
-	Stream & operator << (Stream & os, point<T, N> const & p)
+	template <typename T, std::size_t N>
+	std::ostream & operator << (std::ostream & os, point<T, N> const & p)
 	{
 		os << '(' << p[0];
 		for (std::size_t i = 1; i < N; ++i)
diff --git a/libs/geom/include/psemek/geom/sign.hpp b/libs/geom/include/psemek/geom/sign.hpp
index a5a2dac6..a43fa72e 100644
--- a/libs/geom/include/psemek/geom/sign.hpp
+++ b/libs/geom/include/psemek/geom/sign.hpp
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <psemek/util/assert.hpp>
+#include <psemek/util/io_fwd.hpp>
 
 namespace psemek::geom
 {
@@ -12,8 +13,7 @@ namespace psemek::geom
 		negative = -1,
 	};
 
-	template <typename OStream>
-	OStream & operator << (OStream & o, sign_t s)
+	inline std::ostream & operator << (std::ostream & o, sign_t s)
 	{
 		switch (s)
 		{
diff --git a/libs/geom/include/psemek/geom/simplex.hpp b/libs/geom/include/psemek/geom/simplex.hpp
index f485bdd7..8d91caa3 100644
--- a/libs/geom/include/psemek/geom/simplex.hpp
+++ b/libs/geom/include/psemek/geom/simplex.hpp
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <psemek/util/io_fwd.hpp>
+
 #include <psemek/geom/point.hpp>
 
 #include <type_traits>
@@ -34,8 +36,8 @@ namespace psemek::geom
 	template <typename Point>
 	using triangle = simplex<Point, 2>;
 
-	template <typename Stream, typename Point, std::size_t K>
-	Stream & operator << (Stream & os, simplex<Point, K> const & s)
+	template <typename Point, std::size_t K>
+	std::ostream & operator << (std::ostream & os, simplex<Point, K> const & s)
 	{
 		os << '(' << s[0];
 		for (std::size_t i = 1; i <= K; ++i)
diff --git a/libs/geom/include/psemek/geom/vector.hpp b/libs/geom/include/psemek/geom/vector.hpp
index 64be7975..504d6aac 100644
--- a/libs/geom/include/psemek/geom/vector.hpp
+++ b/libs/geom/include/psemek/geom/vector.hpp
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <psemek/util/io_fwd.hpp>
+
 #include <psemek/geom/detail/array.hpp>
 
 #include <cstddef>
@@ -340,8 +342,8 @@ namespace psemek::geom
 		}
 	}
 
-	template <typename Stream, typename T, std::size_t N>
-	Stream & operator << (Stream & os, vector<T, N> const & v)
+	template <typename T, std::size_t N>
+	std::ostream & operator << (std::ostream & os, vector<T, N> const & v)
 	{
 		if constexpr (N == 0)
 		{
diff --git a/libs/log/include/psemek/log/level.hpp b/libs/log/include/psemek/log/level.hpp
index 77cabba9..27cd0d66 100644
--- a/libs/log/include/psemek/log/level.hpp
+++ b/libs/log/include/psemek/log/level.hpp
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <iostream>
+
 namespace psemek::log
 {
 
@@ -11,8 +13,7 @@ namespace psemek::log
 		error,
 	};
 
-	template <typename Stream>
-	Stream & operator << (Stream & s, level l)
+	inline std::ostream & operator << (std::ostream & s, level l)
 	{
 		switch (l)
 		{
diff --git a/libs/util/include/psemek/util/empty.hpp b/libs/util/include/psemek/util/empty.hpp
index 324e4d9d..bebfb2bd 100644
--- a/libs/util/include/psemek/util/empty.hpp
+++ b/libs/util/include/psemek/util/empty.hpp
@@ -1,12 +1,13 @@
 #pragma once
 
+#include <iostream>
+
 namespace psemek::util
 {
 
 	struct empty{};
 
-	template <typename Stream>
-	Stream & operator << (Stream & os, empty)
+	std::ostream & operator << (std::ostream & os, empty)
 	{
 		os << "empty";
 		return os;
diff --git a/libs/util/include/psemek/util/io_fwd.hpp b/libs/util/include/psemek/util/io_fwd.hpp
new file mode 100644
index 00000000..1d0a7408
--- /dev/null
+++ b/libs/util/include/psemek/util/io_fwd.hpp
@@ -0,0 +1,14 @@
+#pragma once
+
+#include <iostream>
+
+namespace std
+{
+
+	template<typename Char, typename Traits>
+	class basic_istream;
+
+	template<typename Char, typename Traits>
+	class basic_ostream;
+
+}
diff --git a/libs/util/include/psemek/util/statistics.hpp b/libs/util/include/psemek/util/statistics.hpp
index 4c63a89c..8dfbfe98 100644
--- a/libs/util/include/psemek/util/statistics.hpp
+++ b/libs/util/include/psemek/util/statistics.hpp
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <psemek/util/io_fwd.hpp>
+
 #include <cmath>
 #include <limits>
 
@@ -82,8 +84,8 @@ namespace psemek::util
 		return std::sqrt(sum_sqr_ / count_ - m * m);
 	}
 
-	template <typename OStream, typename T>
-	OStream & operator << (OStream & os, statistics<T> const & s)
+	template <typename T>
+	std::ostream & operator << (std::ostream & os, statistics<T> const & s)
 	{
 		os << "mean = " << s.mean() << ", var = " << s.var() << ", range = [" << s.min() << " .. " << s.max() << "]";
 		return os;
diff --git a/tools/test/include/psemek/test/test.hpp b/tools/test/include/psemek/test/test.hpp
index 8c476df8..d60b711e 100644
--- a/tools/test/include/psemek/test/test.hpp
+++ b/tools/test/include/psemek/test/test.hpp
@@ -67,8 +67,8 @@ namespace psemek::test
 
 }
 
-template <typename Stream, typename T>
-Stream & operator << (Stream & s, std::optional<T> const & o)
+template <typename T>
+std::ostream & operator << (std::ostream & s, std::optional<T> const & o)
 {
 	if (o)
 		s << *o;