diff --git a/src/command.cpp b/src/command.cpp
index 959610cd28..d72b55931d 100644
--- a/src/command.cpp
+++ b/src/command.cpp
@@ -26,6 +26,8 @@
 #include "signal_func.h"
 #include "core/backup_type.hpp"
 #include "object_base.h"
+#include "newgrf_text.h"
+#include "string_func.h"
 
 #include "table/strings.h"
 
@@ -735,7 +737,9 @@ CommandCost DoCommandPInternal(TileIndex tile, uint32 p1, uint32 p2, uint32 cmd,
 	 * test and execution have yielded the same result,
 	 * i.e. cost and error state are the same. */
 	if (!test_and_exec_can_differ) {
-		assert(res.GetCost() == res2.GetCost() && res.Failed() == res2.Failed()); // sanity check
+		assert_msg(res.GetCost() == res2.GetCost() && res.Failed() == res2.Failed(),
+				"Command: cmd: 0x%X (%s), Test: %s, Exec: %s", cmd, GetCommandName(cmd),
+				res.AllocSummaryMessage(GB(cmd, 16, 16)), res2.AllocSummaryMessage(GB(cmd, 16, 16))); // sanity check
 	} else if (res2.Failed()) {
 		return_dcpi(res2);
 	}
@@ -803,3 +807,34 @@ void CommandCost::UseTextRefStack(const GRFFile *grffile, uint num_registers)
 		textref_stack[i] = _temp_store.GetValue(0x100 + i);
 	}
 }
+
+char *CommandCost::AllocSummaryMessage(StringID cmd_msg) const
+{
+	char buf[DRAW_STRING_BUFFER];
+	this->WriteSummaryMessage(buf, lastof(buf), cmd_msg);
+	return stredup(buf, lastof(buf));
+}
+
+int CommandCost::WriteSummaryMessage(char *buf, char *last, StringID cmd_msg) const
+{
+	if (this->Succeeded()) {
+		return seprintf(buf, last, "Success: cost: " OTTD_PRINTF64, (int64) this->GetCost());
+	} else {
+		if (this->textref_stack_size > 0) StartTextRefStackUsage(this->textref_stack_grffile, this->textref_stack_size, textref_stack);
+
+		char *b = buf;
+		b += seprintf(b, last, "Failed: cost: " OTTD_PRINTF64, (int64) this->GetCost());
+		if (cmd_msg != 0) {
+			b += seprintf(b, last, " ");
+			b = GetString(b, cmd_msg, last);
+		}
+		if (this->message != INVALID_STRING_ID) {
+			b += seprintf(b, last, " ");
+			b = GetString(b, this->message, last);
+		}
+
+		if (this->textref_stack_size > 0) StopTextRefStackUsage();
+
+		return b - buf;
+	}
+}
diff --git a/src/command_type.h b/src/command_type.h
index f318216acc..1d39ee00a9 100644
--- a/src/command_type.h
+++ b/src/command_type.h
@@ -162,6 +162,21 @@ public:
 	{
 		return !this->success;
 	}
+
+	/**
+	 * @param cmd_msg optional failure string as passed to DoCommand
+	 * @return an allocated string summarising the command result
+	 */
+	char *AllocSummaryMessage(StringID cmd_msg = 0) const;
+
+	/**
+	 * Write a string summarising the command result
+	 * @param buf buffer to write to
+	 * @param last last byte in buffer
+	 * @param cmd_msg optional failure string as passed to DoCommand
+	 * @return the number of bytes written
+	 */
+	int WriteSummaryMessage(char *buf, char *last, StringID cmd_msg = 0) const;
 };
 
 /**
diff --git a/src/openttd.cpp b/src/openttd.cpp
index c149ebbd4d..5e3d2a6c4c 100644
--- a/src/openttd.cpp
+++ b/src/openttd.cpp
@@ -123,6 +123,25 @@ void CDECL error(const char *s, ...)
 	abort();
 }
 
+void CDECL assert_msg_error(int line, const char *file, const char *expr, const char *str, ...)
+{
+	va_list va;
+	char buf[2048];
+
+	char *b = buf;
+	b += seprintf(b, lastof(buf), "Assertion failed at line %i of %s: %s\n\t", line, file, expr);
+
+	va_start(va, str);
+	vseprintf(b, lastof(buf), str, va);
+	va_end(va);
+
+	ShowOSErrorBox(buf, true);
+
+	/* Set the error message for the crash log and then invoke it. */
+	CrashLog::SetErrorMessage(buf);
+	abort();
+}
+
 /**
  * Shows some information on the console/a popup box depending on the OS.
  * @param str the text to show.
diff --git a/src/stdafx.h b/src/stdafx.h
index 4616212f18..78401402e5 100644
--- a/src/stdafx.h
+++ b/src/stdafx.h
@@ -446,6 +446,7 @@ assert_compile(SIZE_MAX >= UINT32_MAX);
 
 void NORETURN CDECL usererror(const char *str, ...) WARN_FORMAT(1, 2);
 void NORETURN CDECL error(const char *str, ...) WARN_FORMAT(1, 2);
+void NORETURN CDECL assert_msg_error(int line, const char *file, const char *expr, const char *str, ...) WARN_FORMAT(4, 5);
 #define NOT_REACHED() error("NOT_REACHED triggered at line %i of %s", __LINE__, __FILE__)
 
 /* For non-debug builds with assertions enabled use the special assertion handler:
@@ -460,6 +461,9 @@ void NORETURN CDECL error(const char *str, ...) WARN_FORMAT(1, 2);
 /* Asserts are enabled if NDEBUG isn't defined, or if we are using MSVC and WITH_ASSERT is defined. */
 #if !defined(NDEBUG) || (defined(_MSC_VER) && defined(WITH_ASSERT))
 	#define OTTD_ASSERT
+	#define assert_msg(expression, ...) if (!(expression)) assert_msg_error(__LINE__, __FILE__, #expression, __VA_ARGS__);
+#else
+	#define assert_msg(expression, ...)
 #endif
 
 #if defined(MORPHOS) || defined(__NDS__) || defined(__DJGPP__)