diff --git a/source/compiler/sc1.c b/source/compiler/sc1.c
index 5a69189..ead5cd6 100644
--- a/source/compiler/sc1.c
+++ b/source/compiler/sc1.c
@@ -649,8 +649,10 @@ int pc_compile(int argc, char *argv[])
     error(13);                  /* no entry point (no public functions) */
 
 cleanup:
-  if (inpf!=NULL)               /* main source file is not closed, do it now */
+  if (inpf!=NULL) {             /* main source file is not closed, do it now */
     pc_closesrc(inpf);
+    inpf=NULL;
+  }
   /* write the binary file (the file is already open) */
   if (!(sc_asmfile || sc_listing) && errnum==0 && jmpcode==0) {
     assert(binf!=NULL);
diff --git a/source/compiler/sc6.c b/source/compiler/sc6.c
index 795c8f0..85c714a 100644
--- a/source/compiler/sc6.c
+++ b/source/compiler/sc6.c
@@ -211,6 +211,21 @@ static char *stripcomment(char *str)
   return str;
 }
 
+static char *stripwhitespace(char *str)
+{
+  if (*str!='\0') {
+    size_t len = strlen(str);
+    size_t i;
+    for (i=len-1; i>=0; i--) {
+      if (!isspace(str[i])) {
+        str[i+1]='\0';
+        break;
+      }
+    }
+  }
+  return str;
+}
+
 static void write_encoded(FILE *fbin,ucell *c,int num)
 {
   #if PAWN_CELL_SIZE == 16
@@ -1016,7 +1031,8 @@ SC_FUNC int assemble(FILE *fout,FILE *fin)
         /* nothing */;
       assert(params>instr);
       i=findopcode(instr,(int)(params-instr));
-      assert(opcodelist[i].name!=NULL);
+      if (opcodelist[i].name==NULL)
+        error(104, stripwhitespace(instr)); /* invalid assembler instruction */
       if (opcodelist[i].segment==pass)
         opcodelist[i].func(fout,skipwhitespace(params),opcodelist[i].opcode);
     } /* while */