diff --git a/libuavcan/include/uavcan/helpers/ostream.hpp b/libuavcan/include/uavcan/helpers/ostream.hpp
index 447b0b9a5e..60edcc010f 100644
--- a/libuavcan/include/uavcan/helpers/ostream.hpp
+++ b/libuavcan/include/uavcan/helpers/ostream.hpp
@@ -36,25 +36,25 @@ public:
     }
 };
 
-OStream& operator<<(OStream& s, long long x)          { std::printf("%lld", x);  return s; }
-OStream& operator<<(OStream& s, unsigned long long x) { std::printf("%llud", x); return s; }
+inline OStream& operator<<(OStream& s, long long x)          { std::printf("%lld", x);  return s; }
+inline OStream& operator<<(OStream& s, unsigned long long x) { std::printf("%llud", x); return s; }
 
-OStream& operator<<(OStream& s, long x)           { std::printf("%ld", x); return s; }
-OStream& operator<<(OStream& s, unsigned long x)  { std::printf("%lu", x); return s; }
+inline OStream& operator<<(OStream& s, long x)           { std::printf("%ld", x); return s; }
+inline OStream& operator<<(OStream& s, unsigned long x)  { std::printf("%lu", x); return s; }
 
-OStream& operator<<(OStream& s, int x)            { std::printf("%d", x);  return s; }
-OStream& operator<<(OStream& s, unsigned int x)   { std::printf("%u", x);  return s; }
+inline OStream& operator<<(OStream& s, int x)            { std::printf("%d", x);  return s; }
+inline OStream& operator<<(OStream& s, unsigned int x)   { std::printf("%u", x);  return s; }
 
-OStream& operator<<(OStream& s, short x)          { return operator<<(s, static_cast<int>(x)); }
-OStream& operator<<(OStream& s, unsigned short x) { return operator<<(s, static_cast<unsigned>(x)); }
+inline OStream& operator<<(OStream& s, short x)          { return operator<<(s, static_cast<int>(x)); }
+inline OStream& operator<<(OStream& s, unsigned short x) { return operator<<(s, static_cast<unsigned>(x)); }
 
-OStream& operator<<(OStream& s, long double x) { std::printf("%Lg", x); return s; }
-OStream& operator<<(OStream& s, double x)      { std::printf("%g", x);  return s; }
-OStream& operator<<(OStream& s, float x)       { return operator<<(s, static_cast<double>(x)); }
+inline OStream& operator<<(OStream& s, long double x) { std::printf("%Lg", x); return s; }
+inline OStream& operator<<(OStream& s, double x)      { std::printf("%g", x);  return s; }
+inline OStream& operator<<(OStream& s, float x)       { return operator<<(s, static_cast<double>(x)); }
 
-OStream& operator<<(OStream& s, char x)        { std::printf("%c", x); return s; }
-OStream& operator<<(OStream& s, const char* x) { std::printf("%s", x); return s; }
+inline OStream& operator<<(OStream& s, char x)        { std::printf("%c", x); return s; }
+inline OStream& operator<<(OStream& s, const char* x) { std::printf("%s", x); return s; }
 
-OStream& operator<<(OStream& s, OStream&(*manip)(OStream&)) { return manip(s); }
+inline OStream& operator<<(OStream& s, OStream&(*manip)(OStream&)) { return manip(s); }
 
 }