diff --git a/src/cl65/main.c b/src/cl65/main.c
index 31d805181..42126e6d7 100644
--- a/src/cl65/main.c
+++ b/src/cl65/main.c
@@ -378,6 +378,14 @@ static void CmdSetOutput (CmdDesc* Cmd, const char* File)
 
 
 
+static void CmdSetAsmOutput (CmdDesc* Cmd, const char* File)
+/* Set the output asm file in a command desc for grc65 */
+{
+    CmdAddArg2 (Cmd, "-s", File);
+}
+
+
+
 static void CmdSetTarget (CmdDesc* Cmd, target_t Target)
 /* Set the output file in a command desc */
 {
@@ -526,12 +534,15 @@ static void Link (void)
 
 
 
-static void AssembleFile (const char* File, unsigned ArgCount)
+static void AssembleFile (const char* File, const char* TmpFile, unsigned ArgCount)
 /* Common routine to assemble a file. Will be called by Assemble() and
 ** AssembleIntermediate(). Adds options common for both routines and
 ** assembles the file. Will remove excess arguments after assembly.
 */
 {
+    /* ObjName may be used for temporary or real filename */
+    char *ObjName;
+
     /* Set the target system */
     CmdSetTarget (&CA65, Target);
 
@@ -541,7 +552,12 @@ static void AssembleFile (const char* File, unsigned ArgCount)
         ** to the file list of the linker. The name of the output
         ** file is that of the input file with ".s" replaced by ".o".
         */
-        char* ObjName = MakeFilename (File, ".o");
+        if (TmpFile) {
+            ObjName = MakeFilename (TmpFile, ".o");
+        } else {
+            ObjName = MakeTmpFilename (".o");
+        }
+        CmdSetOutput (&CA65, ObjName);
         CmdAddFile (&LD65, ObjName);
         /* This is just a temporary file, schedule it for removal */
         CmdAddFile (&RM, ObjName);
@@ -550,11 +566,15 @@ static void AssembleFile (const char* File, unsigned ArgCount)
         /* This is the final step. If an output name is given, set it */
         if (OutputName) {
             CmdSetOutput (&CA65, OutputName);
+        } else {
+            ObjName = MakeFilename (File, ".o");
+            CmdSetOutput (&CA65, ObjName);
+            xfree (ObjName);
         }
     }
 
     /* Add the file as argument for the assembler */
-    CmdAddArg (&CA65, File);
+    CmdAddArg (&CA65, TmpFile ? TmpFile : File);
 
     /* Add a NULL pointer to terminate the argument list */
     CmdAddArg (&CA65, 0);
@@ -568,7 +588,7 @@ static void AssembleFile (const char* File, unsigned ArgCount)
 
 
 
-static void AssembleIntermediate (const char* SourceFile)
+static void AssembleIntermediate (const char* SourceFile, const char* TmpFile)
 /* Assemble an intermediate file which was generated by a previous processing
 ** step with SourceFile as input. The -dep options won't be added and
 ** the intermediate assembler file is removed after assembly.
@@ -578,18 +598,20 @@ static void AssembleIntermediate (const char* SourceFile)
     ** name. It's the same name with the extension replaced by ".s"
     */
     char* AsmName = MakeFilename (SourceFile, ".s");
+    char* AsmTmpName = TmpFile ? MakeFilename(TmpFile, ".s") : NULL;
 
     /* Assemble the intermediate assembler file */
-    AssembleFile (AsmName, CA65.ArgCount);
+    AssembleFile (AsmName, AsmTmpName, CA65.ArgCount);
 
     /* Remove the input file */
-    if (remove (AsmName) < 0) {
+    if (remove (AsmTmpName ? AsmTmpName : AsmName) < 0) {
         Warning ("Cannot remove temporary file '%s': %s",
-                 AsmName, strerror (errno));
+                 AsmTmpName ? AsmTmpName : AsmName, strerror (errno));
     }
 
     /* Free the assembler file name which was allocated from the heap */
     xfree (AsmName);
+    xfree (AsmTmpName);
 }
 
 
@@ -612,7 +634,7 @@ static void Assemble (const char* File)
     }
 
     /* Use the common routine */
-    AssembleFile (File, ArgCount);
+    AssembleFile (File, NULL, ArgCount);
 }
 
 
@@ -620,6 +642,9 @@ static void Assemble (const char* File)
 static void Compile (const char* File)
 /* Compile the given file */
 {
+    /* A temporary file name passed to the assembler */
+    char *TmpFile = NULL;
+
     /* Remember the current compiler argument count */
     unsigned ArgCount = CC65.ArgCount;
 
@@ -657,6 +682,12 @@ static void Compile (const char* File)
     /* Add the file as argument for the compiler */
     CmdAddArg (&CC65, File);
 
+    if (DoAssemble) {
+        /* set a temporary output file name */
+        TmpFile = MakeTmpFilename(".s");
+        CmdSetOutput (&CC65, TmpFile);
+    }
+
     /* Add a NULL pointer to terminate the argument list */
     CmdAddArg (&CC65, 0);
 
@@ -671,7 +702,10 @@ static void Compile (const char* File)
     */
     if (DoAssemble) {
         /* Assemble the intermediate file and remove it */
-        AssembleIntermediate (File);
+        AssembleIntermediate (File, TmpFile);
+        if (TmpFile) {
+            xfree(TmpFile);
+        }
     }
 }
 
@@ -680,6 +714,9 @@ static void Compile (const char* File)
 static void CompileRes (const char* File)
 /* Compile the given geos resource file */
 {
+    /* tmp Asm file name, if needed */
+    char* AsmName = NULL;
+
     /* Remember the current assembler argument count */
     unsigned ArgCount = GRC.ArgCount;
 
@@ -688,6 +725,14 @@ static void CompileRes (const char* File)
     */
     CmdSetTarget (&GRC, Target);
 
+    /* Changes to output file name must come
+    ** BEFORE adding the file
+    */
+    if (DoAssemble && DoLink) {
+        AsmName = MakeTmpFilename(".s");
+        CmdSetAsmOutput(&GRC, AsmName);
+    }
+
     /* Add the file as argument for the resource compiler */
     CmdAddArg (&GRC, File);
 
@@ -705,7 +750,10 @@ static void CompileRes (const char* File)
     */
     if (DoAssemble) {
         /* Assemble the intermediate file and remove it */
-        AssembleIntermediate (File);
+        AssembleIntermediate (File, AsmName);
+        if (AsmName) {
+            xfree(AsmName);
+        }
     }
 }
 
@@ -741,7 +789,7 @@ static void ConvertO65 (const char* File)
     */
     if (DoAssemble) {
         /* Assemble the intermediate file and remove it */
-        AssembleIntermediate (File);
+        AssembleIntermediate (File, NULL);
     }
 }
 
diff --git a/src/common/fname.c b/src/common/fname.c
index 4e4f7c7fa..e67470b33 100644
--- a/src/common/fname.c
+++ b/src/common/fname.c
@@ -33,6 +33,7 @@
 
 
 
+#include <stdio.h>
 #include <string.h>
 
 #include "xmalloc.h"
@@ -115,3 +116,38 @@ char* MakeFilename (const char* Origin, const char* Ext)
     }
     return Out;
 }
+
+
+
+char* MakeTmpFilename (const char* Ext)
+/* Make a new temporary file name from Ext.  tmpnam(3) is called
+** and Ext is appended to generate the filename.
+** The result is placed in a malloc'ed buffer and returned.
+*/
+{
+    char* Out;
+    char Buffer[L_tmpnam * 2]; /* a lazy way to ensure we have space for Ext */
+
+    /*
+    ** gcc emits the following warning here:
+    **
+    ** warning: the use of `tmpnam' is dangerous, better use `mkstemp'
+    **
+    ** however, mkstemp actually opens a file, which we do not want.
+    ** tmpfile() is unsuitable for the same reason.
+    **
+    ** we could write our own version, but then we would have to struggle
+    ** with supporting multiple build environments.
+    **
+    ** tmpnam(3) is safe here, because ca65 / cc65 / ld65 will simply clobber
+    ** an existing file, or exit if with an error if they are unable to.
+    **
+    ** gcc will also complain, if you don't use the return value from tmpnam(3)
+    */
+    strcat(tmpnam(Buffer), Ext);
+
+    Out = xmalloc (strlen (Buffer) + 1);
+    strcpy (Out, Buffer);
+
+    return Out;
+}
diff --git a/src/common/fname.h b/src/common/fname.h
index 1b94d270c..852c4ae56 100644
--- a/src/common/fname.h
+++ b/src/common/fname.h
@@ -59,6 +59,12 @@ char* MakeFilename (const char* Origin, const char* Ext);
 ** The function may be used to create "foo.o" from "foo.s".
 */
 
+char* MakeTmpFilename (const char* Ext);
+/* Make a new temporary file name from Ext.  tmpnam(3) is called
+** and Ext is appended to generate the filename.
+** The result is placed in a malloc'ed buffer and returned.
+*/
+
 
 
 /* End of fname.h */