diff --git a/common/nextpnr.h b/common/nextpnr.h
index 9d46b654..6a45875b 100644
--- a/common/nextpnr.h
+++ b/common/nextpnr.h
@@ -44,7 +44,7 @@
 
 #if defined(__GNUC__) || defined(__clang__)
 #define NPNR_ATTRIBUTE(...) __attribute__((__VA_ARGS__))
-#define NPNR_NORETURN
+#define NPNR_NORETURN __attribute__((noreturn))
 #define NPNR_DEPRECATED __attribute__((deprecated))
 #define NPNR_PACKED_STRUCT(...) __VA_ARGS__ __attribute__((packed))
 #elif defined(_MSC_VER)
@@ -78,8 +78,15 @@ inline void except_assert_impl(bool expr, std::string message, std::string expr_
         throw assertion_failure(message, expr_str, filename, line);
 }
 
+NPNR_NORETURN
+inline void assert_false_impl(std::string message, std::string filename, int line)
+{
+    throw assertion_failure(message, "false", filename, line);
+}
+
 #define NPNR_ASSERT(cond) except_assert_impl((cond), #cond, #cond, __FILE__, __LINE__)
 #define NPNR_ASSERT_MSG(cond, msg) except_assert_impl((cond), msg, #cond, __FILE__, __LINE__)
+#define NPNR_ASSERT_FALSE(msg) assert_false_impl(msg, __FILE__, __LINE__)
 
 struct BaseCtx;
 struct Context;
diff --git a/ice40/bitstream.cc b/ice40/bitstream.cc
index 33c4d97b..98a7a0e4 100644
--- a/ice40/bitstream.cc
+++ b/ice40/bitstream.cc
@@ -36,7 +36,7 @@ const ConfigEntryPOD &find_config(const TileInfoPOD &tile, const std::string &na
             return tile.entries[i];
         }
     }
-    NPNR_ASSERT(false);
+    NPNR_ASSERT_FALSE("unable to find config bit " + name);
 }
 
 std::tuple<int8_t, int8_t, int8_t> get_ieren(const BitstreamInfoPOD &bi, int8_t x, int8_t y, int8_t z)
@@ -124,7 +124,7 @@ void write_asc(const Context *ctx, std::ostream &out)
         out << ".device 5k" << std::endl;
         break;
     default:
-        NPNR_ASSERT(false);
+        NPNR_ASSERT_FALSE("unsupported device type");
     }
     // Set pips
     for (auto pip : ctx->getPips()) {