diff --git a/subprojects/gst-plugins-bad/sys/decklink/gstdecklink.h b/subprojects/gst-plugins-bad/sys/decklink/gstdecklink.h
index dd50e7869d..1c8881b1be 100644
--- a/subprojects/gst-plugins-bad/sys/decklink/gstdecklink.h
+++ b/subprojects/gst-plugins-bad/sys/decklink/gstdecklink.h
@@ -50,7 +50,15 @@
 #include "osx/DeckLinkAPI.h"
 
 #define COMSTR_T CFStringRef
-#define CONVERT_COM_STRING(s) G_STMT_START { CFStringRef _s = (CFStringRef)s; s = (char*) malloc(100); CFStringGetCString(_s, s, 100, kCFStringEncodingUTF8); CFRelease(_s); } G_STMT_END
+#define CONVERT_COM_STRING(s) G_STMT_START { \
+        CFStringRef _s = (CFStringRef)s; \
+        CFIndex _length; \
+        CFStringGetBytes(_s, CFRangeMake(0, CFStringGetLength(_s)), kCFStringEncodingUTF8, 0, FALSE, NULL, 0, &_length); \
+        _length += 1; \
+        s = (char *) malloc(_length); \
+        CFStringGetCString(_s, s, _length, kCFStringEncodingUTF8); \
+        CFRelease(_s); \
+    } G_STMT_END
 #define FREE_COM_STRING(s) free(s);
 #define CONVERT_TO_COM_STRING(s) G_STMT_START { char * _s = (char *)s; s = CFStringCreateWithCString(kCFAllocatorDefault, _s, kCFStringEncodingUTF8); g_free(_s); } G_STMT_END
 #define WINAPI