diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 9d7bdbb4523..be376758b82 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -11192,7 +11192,9 @@ c_finish_return (location_t loc, tree retval, tree origtype)
 	  && valtype != NULL_TREE && TREE_CODE (valtype) != VOID_TYPE)
 	{
 	  no_warning = true;
-	  if (emit_diagnostic (flag_isoc99 ? DK_PEDWARN : DK_WARNING,
+	  if (emit_diagnostic (flag_isoc99 && !flag_pedantic_errors
+			       ? DK_PERMERROR
+			       : flag_isoc99 ? DK_PEDWARN : DK_WARNING,
 			       loc, OPT_Wreturn_mismatch,
 			       "%<return%> with no value,"
 			       " in function returning non-void"))
@@ -11205,7 +11207,7 @@ c_finish_return (location_t loc, tree retval, tree origtype)
       current_function_returns_null = 1;
       bool warned_here;
       if (TREE_CODE (TREE_TYPE (retval)) != VOID_TYPE)
-	warned_here = pedwarn
+	warned_here = pedpermerror
 	  (xloc, OPT_Wreturn_mismatch,
 	   "%<return%> with a value, in function returning void");
       else
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 3a1b9b00f24..6635a136cd9 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -6183,6 +6183,7 @@ that have their own flag:
 -Wimplicit-int @r{(C)}
 -Wint-conversion @r{(C)}
 -Wnarrowing @r{(C++)}
+-Wreturn-mismatch @r{(C)}
 }
 
 The @option{-fpermissive} option is the default for historic C language
@@ -7373,7 +7374,10 @@ Attempting to use the return value of a non-@code{void} function other
 than @code{main} that flows off the end by reaching the closing curly
 brace that terminates the function is undefined.
 
-This warning is specific to C and enabled by default.
+This warning is specific to C and enabled by default.  In C99 and later
+language dialects, it is treated as an error.  It an be downgraded
+to a warning using @option{-fpermissive} (along with other warnings),
+or for just this warning, with @option{-Wno-error=return-mismatch}.
 
 @opindex Wreturn-type
 @opindex Wno-return-type
diff --git a/gcc/testsuite/gcc.dg/20030906-1.c b/gcc/testsuite/gcc.dg/20030906-1.c
index c416f55ee75..6ba5b3d770a 100644
--- a/gcc/testsuite/gcc.dg/20030906-1.c
+++ b/gcc/testsuite/gcc.dg/20030906-1.c
@@ -2,7 +2,7 @@
    Copyright (C) 2003 Free Software Foundation Inc.  */
 
 /* { dg-do compile } */
-/* { dg-options "-O -finline-functions -Wreturn-type" } */
+/* { dg-options "-fpermissive -O -finline-functions -Wreturn-type" } */
 
 extern int i;
 extern int foo (void);
diff --git a/gcc/testsuite/gcc.dg/20030906-1a.c b/gcc/testsuite/gcc.dg/20030906-1a.c
new file mode 100644
index 00000000000..46ca1771a4d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/20030906-1a.c
@@ -0,0 +1,21 @@
+/* Bug 9862 -- Spurious warnings with -finline-functions.
+   Copyright (C) 2003 Free Software Foundation Inc.  */
+
+/* { dg-do compile } */
+/* { dg-options "-O -finline-functions -Wreturn-type" } */
+
+extern int i;
+extern int foo (void);
+extern int bar (void);
+
+int foo (void)
+{
+  if( i ) return 0;
+  else    return 1;
+}
+
+int bar (void)
+{
+  if( i ) return; /* { dg-error "'return' with no value, in function returning non-void" } */
+  else    return 1;
+}		
diff --git a/gcc/testsuite/gcc.dg/20030906-2.c b/gcc/testsuite/gcc.dg/20030906-2.c
index 1191133e6a0..a85d91f46f3 100644
--- a/gcc/testsuite/gcc.dg/20030906-2.c
+++ b/gcc/testsuite/gcc.dg/20030906-2.c
@@ -2,7 +2,7 @@
    Copyright (C) 2003 Free Software Foundation Inc.  */
 
 /* { dg-do compile } */
-/* { dg-options "-O -finline-functions -Wreturn-type" } */
+/* { dg-options "-fpermissive -O -finline-functions -Wreturn-type" } */
 
 extern int i;
 extern int foo (void);
diff --git a/gcc/testsuite/gcc.dg/20030906-2a.c b/gcc/testsuite/gcc.dg/20030906-2a.c
new file mode 100644
index 00000000000..a6ffbacb46d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/20030906-2a.c
@@ -0,0 +1,21 @@
+/* Bug 9862 -- Spurious warnings with -finline-functions.
+   Copyright (C) 2003 Free Software Foundation Inc.  */
+
+/* { dg-do compile } */
+/* { dg-options "-O -finline-functions -Wreturn-type" } */
+
+extern int i;
+extern int foo (void);
+extern int bar (void);
+
+int foo (void)
+{
+  if( i ) return; /* { dg-error "'return' with no value, in function returning non-void" } */
+  else    return 1;
+}
+
+int bar (void)
+{
+  if( i ) return 0;
+  else    return 1;
+}
diff --git a/gcc/testsuite/gcc.dg/Wreturn-mismatch-1.c b/gcc/testsuite/gcc.dg/Wreturn-mismatch-1.c
index 3bad847ecf7..aef6782cbeb 100644
--- a/gcc/testsuite/gcc.dg/Wreturn-mismatch-1.c
+++ b/gcc/testsuite/gcc.dg/Wreturn-mismatch-1.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "" } */
+/* { dg-options "-fpermissive" } */
 
 void f1 (void);
 
diff --git a/gcc/testsuite/gcc.dg/Wreturn-mismatch-1a.c b/gcc/testsuite/gcc.dg/Wreturn-mismatch-1a.c
new file mode 100644
index 00000000000..70c7c9ddb86
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wreturn-mismatch-1a.c
@@ -0,0 +1,40 @@
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+void f1 (void);
+
+int
+f2 (void)
+{
+  f1 ();
+}
+
+static inline int
+f3 (void)
+{
+  f1 ();
+}
+
+void
+f4 (void)
+{
+  return 1; /* { dg-error "'return' with a value\[^\n\r\]*-Wreturn-mismatch" } */
+}
+
+void
+f5 (void)
+{
+  return f1 (); /* { dg-bogus "ISO C" } */
+}
+
+int
+f6 (void)
+{
+  return; /* { dg-error "'return' with no value\[^\n\r\]*-Wreturn-mismatch" } */
+}
+
+int
+f7 (void)
+{
+  return f1 (); /* { dg-error "void value not ignored as it ought to be" } */
+}
diff --git a/gcc/testsuite/gcc.dg/Wreturn-mismatch-2.c b/gcc/testsuite/gcc.dg/Wreturn-mismatch-2.c
index 49eb5a5a95c..08811024b7e 100644
--- a/gcc/testsuite/gcc.dg/Wreturn-mismatch-2.c
+++ b/gcc/testsuite/gcc.dg/Wreturn-mismatch-2.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-Wall" } */
+/* { dg-options "-fpermissive -Wall" } */
 
 void f1 (void);
 
diff --git a/gcc/testsuite/gcc.dg/Wreturn-mismatch-2a.c b/gcc/testsuite/gcc.dg/Wreturn-mismatch-2a.c
new file mode 100644
index 00000000000..836651ed925
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wreturn-mismatch-2a.c
@@ -0,0 +1,41 @@
+/* { dg-do compile } */
+/* { dg-options "-Wall" } */
+
+void f1 (void);
+
+int
+f2 (void)
+{
+  f1 ();
+} /* { dg-warning "control reaches end of non-void\[^\n\r\]*-Wreturn-type" } */
+
+static inline int
+f3 (void)
+{
+  f1 ();
+} /* { dg-warning "no return statement in function\[^\n\r\]*-Wreturn-type" } */
+
+void
+f4 (void)
+{
+  return 1; /* { dg-error "with a value,\[^\n\r\]*-Wreturn-mismatch" } */
+}
+
+void
+f5 (void)
+{
+  return f1 ();
+}
+
+int
+f6 (void)
+{
+  return; /* { dg-error "with no value,\[^\n\r\]*Wreturn-mismatch" } */
+}
+
+int
+f7 (void)
+{
+  return f1 (); /* { dg-error "void value not ignored as it ought to be" } */
+} /* { dg-warning "control reaches end of non-void\[^\n\r\]*-Wreturn-type" } */
+
diff --git a/gcc/testsuite/gcc.dg/diagnostic-range-bad-return-2.c b/gcc/testsuite/gcc.dg/diagnostic-range-bad-return-2.c
new file mode 100644
index 00000000000..2fe8d341dba
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/diagnostic-range-bad-return-2.c
@@ -0,0 +1,52 @@
+/* { dg-options "-fdiagnostics-show-caret -Wreturn-local-addr" } */
+
+int *address_of_local (void)
+{
+  int some_local;
+  return &some_local; /* { dg-warning "function returns address of local variable" } */
+/* { dg-begin-multiline-output "" }
+   return &some_local;
+          ^~~~~~~~~~~
+   { dg-end-multiline-output "" } */
+}
+
+void surplus_return_when_void_1 (void)
+{
+  return 500; /* { dg-error "'return' with a value, in function returning void" } */
+/* { dg-begin-multiline-output "" }
+   return 500;
+          ^~~
+   { dg-end-multiline-output "" } */
+/* { dg-begin-multiline-output "" }
+ void surplus_return_when_void_1 (void)
+      ^~~~~~~~~~~~~~~~~~~~~~~~~~
+   { dg-end-multiline-output "" } */
+}
+
+void surplus_return_when_void_2 (int i, int j)
+{
+  return i * j; /* { dg-error "'return' with a value, in function returning void" } */
+/* { dg-begin-multiline-output "" }
+   return i * j;
+          ~~^~~
+   { dg-end-multiline-output "" } */
+/* { dg-begin-multiline-output "" }
+ void surplus_return_when_void_2 (int i, int j)
+      ^~~~~~~~~~~~~~~~~~~~~~~~~~
+   { dg-end-multiline-output "" } */
+}
+
+int missing_return_value (void)
+{
+  return; /* { dg-error "'return' with no value, in function returning non-void" } */
+/* { dg-begin-multiline-output "" }
+   return;
+   ^~~~~~
+   { dg-end-multiline-output "" } */
+/* { dg-begin-multiline-output "" }
+ int missing_return_value (void)
+     ^~~~~~~~~~~~~~~~~~~~
+   { dg-end-multiline-output "" } */
+/* TODO: ideally we'd underline the return type i.e. "int", but that
+   location isn't captured.  */
+}
diff --git a/gcc/testsuite/gcc.dg/diagnostic-range-bad-return.c b/gcc/testsuite/gcc.dg/diagnostic-range-bad-return.c
index 063fdf1f636..b74481b870c 100644
--- a/gcc/testsuite/gcc.dg/diagnostic-range-bad-return.c
+++ b/gcc/testsuite/gcc.dg/diagnostic-range-bad-return.c
@@ -1,4 +1,4 @@
-/* { dg-options "-fdiagnostics-show-caret -Wreturn-local-addr" } */
+/* { dg-options "-fpermissive -fdiagnostics-show-caret -Wreturn-local-addr" } */
 
 int *address_of_local (void)
 {
diff --git a/gcc/testsuite/gcc.dg/pr105635-2.c b/gcc/testsuite/gcc.dg/pr105635-2.c
index 807eef0b7cd..019dbc7e557 100644
--- a/gcc/testsuite/gcc.dg/pr105635-2.c
+++ b/gcc/testsuite/gcc.dg/pr105635-2.c
@@ -7,5 +7,5 @@ void foo (int, int[*]);	/* { dg-message "previous declaration of 'foo' with type
 foo (int x, int y)	/* { dg-error "return type defaults to 'int'" } */
 {			/* { dg-warning "conflicting types for 'foo'" "" { target *-*-* } .-1 } */
 			/* { dg-message "declared here" "" { target *-*-* } .-2 } */
-  return (x >= 0) != (y < 0);	/* { dg-warning "'return' with a value, in function returning void" } */
+  return (x >= 0) != (y < 0);	/* { dg-error "'return' with a value, in function returning void" } */
 }
diff --git a/gcc/testsuite/gcc.dg/pr23075-2.c b/gcc/testsuite/gcc.dg/pr23075-2.c
new file mode 100644
index 00000000000..0702ddf1a66
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr23075-2.c
@@ -0,0 +1,14 @@
+/* PR c/23075 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wreturn-type" } */
+
+int
+foo (void)
+{
+  return;	/* { dg-error "with no value" } */
+}		/* { dg-bogus "control reaches end" } */
+
+int
+bar (void)
+{
+}		/* { dg-warning "control reaches end" } */
diff --git a/gcc/testsuite/gcc.dg/pr23075.c b/gcc/testsuite/gcc.dg/pr23075.c
index 2d85fb0650f..28baf41006a 100644
--- a/gcc/testsuite/gcc.dg/pr23075.c
+++ b/gcc/testsuite/gcc.dg/pr23075.c
@@ -1,6 +1,6 @@
 /* PR c/23075 */
 /* { dg-do compile } */
-/* { dg-options "-O2 -Wreturn-type" } */
+/* { dg-options "-O2 -fpermissive -Wreturn-type" } */
 
 int
 foo (void)
diff --git a/gcc/testsuite/gcc.dg/pr29521-a.c b/gcc/testsuite/gcc.dg/pr29521-a.c
new file mode 100644
index 00000000000..2c6a48b7e30
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr29521-a.c
@@ -0,0 +1,15 @@
+/* PR 29521 : warning for return with expression in function returning void */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+void func (void) { }
+
+void func2 (void)
+{
+  return func ();
+}
+
+void func3 (void)
+{
+  return 1;  /* { dg-error "'return' with a value" } */
+}
diff --git a/gcc/testsuite/gcc.dg/pr29521.c b/gcc/testsuite/gcc.dg/pr29521.c
index b6fb535fab7..cd431514ed2 100644
--- a/gcc/testsuite/gcc.dg/pr29521.c
+++ b/gcc/testsuite/gcc.dg/pr29521.c
@@ -1,6 +1,6 @@
 /* PR 29521 : warning for return with expression in function returning void */
 /* { dg-do compile } */
-/* { dg-options "" } */
+/* { dg-options "-fpermissive" } */
 
 void func (void) { }
 
diff --git a/gcc/testsuite/gcc.dg/pr67730-a.c b/gcc/testsuite/gcc.dg/pr67730-a.c
new file mode 100644
index 00000000000..08737cc9811
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr67730-a.c
@@ -0,0 +1,11 @@
+/* PR c/67730 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+#include <stddef.h>
+
+void
+fn1 (void)
+{
+  return NULL; /* { dg-error "10:.return. with a value" } */
+}
diff --git a/gcc/testsuite/gcc.dg/pr67730.c b/gcc/testsuite/gcc.dg/pr67730.c
index 54d73a62cf8..cc51858c531 100644
--- a/gcc/testsuite/gcc.dg/pr67730.c
+++ b/gcc/testsuite/gcc.dg/pr67730.c
@@ -1,6 +1,6 @@
 /* PR c/67730 */
 /* { dg-do compile } */
-/* { dg-options "" } */
+/* { dg-options "-fpermissive" } */
 
 #include <stddef.h>
 
diff --git a/gcc/testsuite/gcc.target/powerpc/conditional-return.c b/gcc/testsuite/gcc.target/powerpc/conditional-return.c
index 6b3ef5f52ca..c6491216752 100644
--- a/gcc/testsuite/gcc.target/powerpc/conditional-return.c
+++ b/gcc/testsuite/gcc.target/powerpc/conditional-return.c
@@ -1,7 +1,7 @@
 /* Check that a conditional return is used.  */
 
 /* { dg-do compile } */
-/* { dg-options "-O2 -w" } */
+/* { dg-options "-O2 -fpermissive -w" } */
 
 /* { dg-final { scan-assembler {\mbeqlr\M} } } */
 
