diff --git a/src/library/grDevices/src/Makefile.win b/src/library/grDevices/src/Makefile.win
index b2c068f3c62..769cdb75cd8 100644
--- a/src/library/grDevices/src/Makefile.win
+++ b/src/library/grDevices/src/Makefile.win
@@ -27,7 +27,8 @@ PKG_CPPFLAGS = -I$(R_HOME)/src/include -DHAVE_CONFIG_H
 devPS-CPPFLAGS = -I"$(EXT_LIBS)/include" -I$(R_HOME)/src/gnuwin32
 
 ## devWindows needs opt.h, console.h, rui.h and graphapp headers
-arch_DEFS = -DR_ARCH='"$(R_ARCH)"'
+## remove slash to avoid Msys2 path conversion
+arch_DEFS = -DR_ARCH='"$(subst /,,$(R_ARCH))"'
 devWindows-CPPFLAGS = -I$(R_HOME)/src/gnuwin32 -I$(R_HOME)/src/extra $(arch_DEFS)
 
 winbitmap-CPPFLAGS = -DHAVE_PNG -DHAVE_JPEG -DHAVE_TIFF -I"$(EXT_LIBS)/include"
diff --git a/src/library/grDevices/src/devWindows.c b/src/library/grDevices/src/devWindows.c
index b6216c4ffd3..58c84e4be15 100644
--- a/src/library/grDevices/src/devWindows.c
+++ b/src/library/grDevices/src/devWindows.c
@@ -3951,7 +3951,7 @@ static int Load_Rcairo_Dll()
 {
     if (!RcairoAlreadyLoaded) {
 	size_t needed = strlen(R_HomeDir())
-	                + strlen("/library/grDevices/libs")
+	                + strlen("/library/grDevices/libs/")
 			+ strlen(R_ARCH)
 			+ strlen("/winCairo.dll") + 1;
 	char *szFullPath = malloc(needed);
@@ -3960,7 +3960,7 @@ static int Load_Rcairo_Dll()
 	    return -1;
 	}
 	strcpy(szFullPath, R_HomeDir());
-	strcat(szFullPath, "/library/grDevices/libs");
+	strcat(szFullPath, "/library/grDevices/libs/");
 	strcat(szFullPath, R_ARCH);
 	strcat(szFullPath, "/winCairo.dll");
 	if (((hRcairoDll = LoadLibrary(szFullPath)) != NULL) &&