diff --git a/src/rt/rust.cpp b/src/rt/rust.cpp
index 37398655190..2200df11067 100644
--- a/src/rt/rust.cpp
+++ b/src/rt/rust.cpp
@@ -94,6 +94,16 @@ rust_srv::fatal(char const *expr, char const *file, size_t line)
     exit(1);
 }
 
+void
+rust_srv::warning(char const *expr, char const *file, size_t line)
+{
+    char buf[1024];
+    snprintf(buf, sizeof(buf),
+             "warning: '%s', at: %s:%d",
+             expr, file, (int)line);
+    log(buf);
+}
+
 rust_srv *
 rust_srv::clone()
 {
diff --git a/src/rt/rust.h b/src/rt/rust.h
index c65d0eb1e96..9a61dca71fe 100644
--- a/src/rt/rust.h
+++ b/src/rt/rust.h
@@ -25,6 +25,7 @@ struct rust_srv {
 
     virtual void log(char const *);
     virtual void fatal(char const *, char const *, size_t);
+    virtual void warning(char const *, char const *, size_t);
     virtual void *malloc(size_t);
     virtual void *realloc(void *, size_t);
     virtual void free(void *);
diff --git a/src/rt/rust_internal.h b/src/rt/rust_internal.h
index 78ba85e8859..bd9be504244 100644
--- a/src/rt/rust_internal.h
+++ b/src/rt/rust_internal.h
@@ -44,10 +44,12 @@ extern "C" {
 #error "Target CPU not supported."
 #endif
 
-#define I(dom, e) ((e) ? (void)0 :                           \
+#define I(dom, e) ((e) ? (void)0 :                             \
                    (dom)->srv->fatal(#e, __FILE__, __LINE__))
+#define W(dom, e, s) ((e) ? (void)0 :                             \
+                   (dom)->srv->warning(#e " : " #s, __FILE__, __LINE__))
 
-#define A(dom, e, s) ((e) ? (void)0 :                                    \
+#define A(dom, e, s) ((e) ? (void)0 :                          \
                       (dom)->srv->fatal(#e " : " #s, __FILE__, __LINE__))
 
 struct rust_task;