diff --git a/lib/system.nim b/lib/system.nim
index 0f0349fba6..cb0e1c85c7 100644
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -3116,3 +3116,27 @@ proc arrayWithDefault*[T](size: static int): array[size, T] {.noinit, nodestroy,
   ## Creates a new array filled with `default(T)`.
   for i in 0..size-1:
     result[i] = default(T)
+
+when hostOS == "standalone":
+  # Include panicoverride.nim late so users can use the full extent of the
+  # language in their custom panic handlers (e.g. macros).
+  # Users define `proc panic(msg: string)` and `proc rawoutput(msg: string)`.
+  include "$projectpath/panicoverride"
+
+  when not declared(panic):
+    {.error:
+      "a panic proc with the following signature must be provided " &
+      "when compiling with --os:standalone: " &
+      "`proc panic(msg: string) {.nimcall.}`".}
+
+  when not declared(rawoutput):
+     {.error:
+      "a rawoutput proc with the following signature must be provided " &
+      "when compiling with --os:standalone: " &
+      "`proc rawoutput(msg: string) {.nimcall.}`".}
+
+  # Wrappers with exportc that fatal.nim references via importc.
+  # This way panicoverride keeps old API and can still be included without
+  # ssymbols being duplicated.
+  proc nimPanic(s: string) {.exportc, noreturn.} = panic(s)
+  proc nimRawoutput(s: string) {.exportc.} = rawoutput(s)
diff --git a/lib/system/fatal.nim b/lib/system/fatal.nim
index 25c05e52d9..900ffa9400 100644
--- a/lib/system/fatal.nim
+++ b/lib/system/fatal.nim
@@ -14,14 +14,23 @@ const
   quirkyExceptions = compileOption("exceptions", "quirky")
 
 when hostOS == "standalone":
-  include "$projectpath/panicoverride"
+  # These procs are defined in panicoverride.nim, which gets included at end
+  # of system.nim with exportc.
+  proc nimPanic(msg: string) {.importc: "nimPanic", noreturn.}
+  proc nimRawoutput(msg: string) {.importc: "nimRawoutput".}
 
-  func sysFatal(exceptn: typedesc[Defect], message: string) {.inline.} =
-    panic(message)
+  proc sysFatal(exceptn: typedesc[Defect], message: string) {.inline, noreturn, raises: [], tags: [].} =
+    {.cast(noSideEffect).}:
+      {.cast(raises: []).}:
+        {.cast(tags: []).}:
+          nimPanic(message)
 
-  func sysFatal(exceptn: typedesc[Defect], message, arg: string) {.inline.} =
-    rawoutput(message)
-    panic(arg)
+  proc sysFatal(exceptn: typedesc[Defect], message, arg: string) {.inline, noreturn, raises: [], tags: [].} =
+    {.cast(noSideEffect).}:
+      {.cast(raises: []).}:
+        {.cast(tags: []).}:
+          nimRawoutput(message)
+          nimPanic(arg)
 
 elif quirkyExceptions and not defined(nimscript):
   import ansi_c
diff --git a/tests/assert/panicoverride.nim b/tests/assert/panicoverride.nim
index 53ad64215b..573c23ea88 100644
--- a/tests/assert/panicoverride.nim
+++ b/tests/assert/panicoverride.nim
@@ -5,11 +5,11 @@ proc exit(code: cint) {.importc, header:"stdlib.h".}
 
 {.push stack_trace: off, profiler:off.}
 
-proc rawoutput(s: cstring) =
-  printf("RAW: %s\n", s)
-  
-proc panic(s: cstring) {.noreturn.} =
-  printf("PANIC: %s\n", s)
+proc rawoutput(s: string) =
+  printf("RAW: %s\n", s.cstring)
+
+proc panic(s: string) {.noreturn.} =
+  printf("PANIC: %s\n", s.cstring)
   exit(0)
 
 {.pop.}
\ No newline at end of file
diff --git a/tests/avr/panicoverride.nim b/tests/avr/panicoverride.nim
index 770933ddd4..3f2eb1d6eb 100644
--- a/tests/avr/panicoverride.nim
+++ b/tests/avr/panicoverride.nim
@@ -4,9 +4,9 @@ proc exit(code: int) {.importc, header: "<stdlib.h>", cdecl.}
 {.push stack_trace: off, profiler:off.}
 
 proc rawoutput(s: string) =
-  printf("%s\n", s)
+  printf("%s\n", s.cstring)
 
-proc panic(s: string) =
+proc panic(s: string) {.noreturn.} =
   rawoutput(s)
   exit(1)
 
diff --git a/tests/errmsgs/t14444.nim b/tests/errmsgs/t14444.nim
index 27365236ed..c9b9049323 100644
--- a/tests/errmsgs/t14444.nim
+++ b/tests/errmsgs/t14444.nim
@@ -3,7 +3,7 @@ discard """
   exitcode: "1"
   output: '''
 t14444.nim(13)           t14444
-fatal.nim(53)            sysFatal
+fatal.nim(62)            sysFatal
 Error: unhandled exception: index out of bounds, the container is empty [IndexDefect]
 '''
 """
diff --git a/tests/errmsgs/t23536.nim b/tests/errmsgs/t23536.nim
index d8f1433331..5dd0f6e0ce 100644
--- a/tests/errmsgs/t23536.nim
+++ b/tests/errmsgs/t23536.nim
@@ -8,7 +8,7 @@ t23536.nim(22)           t23536
 t23536.nim(17)           foo
 assertions.nim(45)       failedAssertImpl
 assertions.nim(40)       raiseAssert
-fatal.nim(53)            sysFatal
+fatal.nim(62)            sysFatal
 """
 
 
diff --git a/tests/errmsgs/t24974.nim b/tests/errmsgs/t24974.nim
index 39d473a89e..cfbb138c87 100644
--- a/tests/errmsgs/t24974.nim
+++ b/tests/errmsgs/t24974.nim
@@ -6,7 +6,7 @@ t24974.nim(19)           d
 t24974.nim(16)           s
 assertions.nim(45)       failedAssertImpl
 assertions.nim(40)       raiseAssert
-fatal.nim(53)            sysFatal
+fatal.nim(62)            sysFatal
 Error: unhandled exception: t24974.nim(16, 26) `false`  [AssertionDefect]
 '''
 """
diff --git a/tests/exception/t22469.nim b/tests/exception/t22469.nim
index a76c749678..368890c208 100644
--- a/tests/exception/t22469.nim
+++ b/tests/exception/t22469.nim
@@ -3,7 +3,7 @@ discard """
   output: '''
 First top-level statement of ModuleB
 m22469.nim(3)            m22469
-fatal.nim(53)            sysFatal
+fatal.nim(62)            sysFatal
 Error: unhandled exception: over- or underflow [OverflowDefect]
 '''
 """
diff --git a/tests/gc/panicoverride.nim b/tests/gc/panicoverride.nim
index 0f28b0b72b..9e3b4785c8 100644
--- a/tests/gc/panicoverride.nim
+++ b/tests/gc/panicoverride.nim
@@ -5,7 +5,7 @@ proc exit(code: int) {.importc, header: "<stdlib.h>", cdecl.}
 {.push stack_trace: off, profiler:off.}
 
 proc rawoutput(s: string) =
-  printf("%s\n", s)
+  printf("%s\n", s.cstring)
 
 proc panic(s: string) {.noreturn.} =
   rawoutput(s)
diff --git a/tests/manyloc/standalone/barebone.nim b/tests/manyloc/standalone/barebone.nim
index 487f6da650..9fbebcba0a 100644
--- a/tests/manyloc/standalone/barebone.nim
+++ b/tests/manyloc/standalone/barebone.nim
@@ -1,7 +1,7 @@
 discard """
 ccodecheck: "\\i !@('systemInit')"
 ccodecheck: "\\i !@('systemDatInit')"
-output: "hello"
+output: "hi 4778"
 """
 # bug  #2041: Macros need to be available for os:standalone!
 import macros
diff --git a/tests/manyloc/standalone/panicoverride.nim b/tests/manyloc/standalone/panicoverride.nim
index c0b8bb030e..2b6b34d434 100644
--- a/tests/manyloc/standalone/panicoverride.nim
+++ b/tests/manyloc/standalone/panicoverride.nim
@@ -5,7 +5,7 @@ proc exit(code: int) {.importc, header: "<stdlib.h>", cdecl.}
 {.push stack_trace: off, profiler:off.}
 
 proc rawoutput(s: string) =
-  printf("%s\n", s)
+  printf("%s\n", s.cstring)
 
 proc panic(s: string) {.noreturn.} =
   rawoutput(s)
diff --git a/tests/manyloc/standalone2/panicoverride.nim b/tests/manyloc/standalone2/panicoverride.nim
index c0b8bb030e..2b6b34d434 100644
--- a/tests/manyloc/standalone2/panicoverride.nim
+++ b/tests/manyloc/standalone2/panicoverride.nim
@@ -5,7 +5,7 @@ proc exit(code: int) {.importc, header: "<stdlib.h>", cdecl.}
 {.push stack_trace: off, profiler:off.}
 
 proc rawoutput(s: string) =
-  printf("%s\n", s)
+  printf("%s\n", s.cstring)
 
 proc panic(s: string) {.noreturn.} =
   rawoutput(s)