Index: src/OFCondition.m
==================================================================
--- src/OFCondition.m
+++ src/OFCondition.m
@@ -17,10 +17,11 @@
 
 #include <errno.h>
 
 #import "OFCondition.h"
 #import "OFDate.h"
+#import "OFString.h"
 
 #import "OFBroadcastConditionFailedException.h"
 #import "OFConditionStillWaitingException.h"
 #import "OFInitializationFailedException.h"
 #import "OFSignalConditionFailedException.h"

Index: src/macros.h
==================================================================
--- src/macros.h
+++ src/macros.h
@@ -357,16 +357,17 @@
 			objc_error("ObjFWRT @ " __FILE__ ":"		\
 			    OF_STRINGIFY(__LINE__),			\
 			    "Failed to ensure condition:\n" #cond);	\
 	} while(0)
 #else
+@class OFConstantString;
+extern void OFLog(OFConstantString *_Nonnull, ...);
 # define OFEnsure(cond)							\
 	do {								\
 		if OF_UNLIKELY (!(cond)) {				\
-			fprintf(stderr, "Failed to ensure condition "	\
-			    "in " __FILE__ ":%d:\n" #cond "\n",		\
-			    __LINE__);					\
+			OFLog(@"Failed to ensure condition in "		\
+			    @__FILE__ ":%d: " @#cond, __LINE__);	\
 			abort();					\
 		}							\
 	} while (0)
 #endif
 

Index: src/platform/AmigaOS/OFPlainThread.m
==================================================================
--- src/platform/AmigaOS/OFPlainThread.m
+++ src/platform/AmigaOS/OFPlainThread.m
@@ -18,10 +18,11 @@
 #include <assert.h>
 #include <errno.h>
 
 #import "OFPlainThread.h"
 #import "OFData.h"
+#import "OFString.h"
 #import "OFTLSKey.h"
 
 #include <dos/dostags.h>
 #include <proto/dos.h>
 #include <proto/exec.h>