diff --git a/compiler/docgen.nim b/compiler/docgen.nim
index d774fd50891e7..005bbbe92a957 100644
--- a/compiler/docgen.nim
+++ b/compiler/docgen.nim
@@ -216,13 +216,21 @@ proc newDocumentor*(filename: AbsoluteFile; cache: IdentCache; conf: ConfigRef,
       # Include the current file if we're parsing a nim file
       let importStmt = if d.isPureRst: "" else: "import \"$1\"\n" % [d.filename.replace("\\", "/")]
       writeFile(outp, importStmt & content)
-      let c = if cmd.startsWith("nim <backend> "): os.getAppFilename() & " " & $conf.backend & cmd.substr("nim <backend>".len)
-              elif cmd.startsWith("nim "): os.getAppFilename() & cmd.substr("nim".len)
-              else: cmd
-      let c2 = c % quoteShell(outp)
-      rawMessage(conf, hintExecuting, c2)
-      if execShellCmd(c2) != status:
-        rawMessage(conf, errGenerated, "executing of external program failed: " & c2)
+
+      proc interpSnippetCmd(cmd: string): string =
+        result = cmd
+        # backward compatibility hacks; interpolation commands should explicitly use `$`
+        result = result.replace("nim ", "$nim")
+        result = result.replace("$1", "$options")
+        result = result % [
+          "nim", os.getAppFilename().quoteShell,
+          "backend", $d.conf.backend,
+          "options", outp.quoteShell,
+        ]
+      let cmd = cmd.interpSnippetCmd
+      rawMessage(conf, hintExecuting, cmd)
+      if execShellCmd(cmd) != status:
+        rawMessage(conf, errGenerated, "executing of external program failed: " & cmd)
   result.emitted = initIntSet()
   result.destFile = getOutFile2(conf, presentationPath(conf, filename),
                                 outExt, htmldocsDir, false)
diff --git a/compiler/main.nim b/compiler/main.nim
index 4fc92b06a2c6a..8e6e2c7e3804e 100644
--- a/compiler/main.nim
+++ b/compiler/main.nim
@@ -196,11 +196,10 @@ proc mainCommand*(graph: ModuleGraph) =
   when false: setOutDir(conf)
   if optUseNimcache in conf.globalOptions: setOutDir(conf)
 
-  proc customizeForBackend(backend2: TBackend) =
+  proc customizeForBackend() =
     ## sets backend specific options but don't compile to backend yet
-    conf.backend = backend2
-    defineSymbol(graph.config.symbols, $backend2)
-    case backend2
+    defineSymbol(graph.config.symbols, $conf.backend)
+    case conf.backend
     of backendC:
       if conf.exc == excNone: conf.exc = excSetjmp
     of backendCpp:
@@ -221,8 +220,11 @@ proc mainCommand*(graph: ModuleGraph) =
 
   proc compileToBackend(backend: TBackend = conf.backend, cmd = cmdCompileToBackend) =
     commandAlreadyProcessed = true
-    customizeForBackend(backend)
     conf.cmd = cmd
+    if conf.backend == backendInvalid:
+      # only set backend if wasn't already set, to allow override via `nim c -b:cpp`
+      conf.backend = backend
+    customizeForBackend()
     case conf.backend
     of backendC: commandCompileToC(graph)
     of backendCpp: commandCompileToC(graph)
@@ -238,7 +240,7 @@ proc mainCommand*(graph: ModuleGraph) =
   of "js", "compiletojs": compileToBackend(backendJs)
   else:
     # this ensures all other commands call this
-    customizeForBackend(conf.backend)
+    customizeForBackend()
 
   ## process all other commands
   case conf.command.normalize
diff --git a/compiler/options.nim b/compiler/options.nim
index 3e6c7989fee27..3ff1a7a22f5bb 100644
--- a/compiler/options.nim
+++ b/compiler/options.nim
@@ -419,7 +419,7 @@ proc newConfigRef*(): ConfigRef =
     cIncludes: @[],   # directories to search for included files
     cLibs: @[],       # directories to search for lib files
     cLinkedLibs: @[],  # libraries to link
-    backend: backendC,
+    backend: backendInvalid,
     externalToLink: @[],
     linkOptionsCmd: "",
     compileOptionsCmd: @[],
diff --git a/lib/packages/docutils/rstgen.nim b/lib/packages/docutils/rstgen.nim
index edd987a76ca00..816d724ef0393 100644
--- a/lib/packages/docutils/rstgen.nim
+++ b/lib/packages/docutils/rstgen.nim
@@ -865,7 +865,7 @@ proc parseCodeBlockField(d: PDoc, n: PRstNode, params: var CodeBlockParams) =
   of "test":
     params.testCmd = n.getFieldValue.strip
     if params.testCmd.len == 0:
-      params.testCmd = "nim <backend> -r $1" # The nim backend is auto-set in docgen.nim
+      params.testCmd = "$nim r --backend:$backend $options" # see `interpSnippetCmd`
     else:
       params.testCmd = unescape(params.testCmd)
   of "status", "exitcode":
diff --git a/tests/misc/mimportcpp.nim b/tests/misc/mbackend.nim
similarity index 55%
rename from tests/misc/mimportcpp.nim
rename to tests/misc/mbackend.nim
index 842c89857bbd7..e38eb2d3e8a9e 100644
--- a/tests/misc/mimportcpp.nim
+++ b/tests/misc/mbackend.nim
@@ -3,11 +3,18 @@ We can't merge this test inside a `when defined(cpp)` because some bug that was
 fixed would not trigger in that case.
 ]#
 
-## bugfix 1: this used to CT error with: Error: unhandled exception: mimportcpp.nim(6, 18) `defined(cpp)`
-static: doAssert defined(cpp)
+import std/compilesettings
+import std/unittest
 
-## checks that `--backend:c` has no side effect (ie, can be overridden by subsequent commands)
-static: doAssert not defined(c)
+static:
+  ## bugfix 1: this used to CT error with: Error: unhandled exception: mimportcpp.nim(6, 18) `defined(cpp)`
+  doAssert defined(cpp)
+  doAssert querySetting(backend) == "cpp"
+
+  ## checks that `--backend:c` has no side effect (ie, can be overridden by subsequent commands)
+  doAssert not defined(c)
+  doAssert not defined(js)
+  doAssert not defined(js)
 
 type
   std_exception {.importcpp: "std::exception", header: "<exception>".} = object
diff --git a/tests/trunner.nim b/tests/trunner.nim
index a32ba3633c179..e89606bf7f1b5 100644
--- a/tests/trunner.nim
+++ b/tests/trunner.nim
@@ -123,15 +123,18 @@ else: # don't run twice the same test
       let cmd = fmt"{nim} r --backend:{mode} --hints:off --nimcache:{nimcache} {file}"
       check execCmdEx(cmd) == ("ok3\n", 0)
 
-  block: # some importc tests
-    # issue #14314
-    let file = testsDir / "misc/mimportc.nim"
-    let cmd = fmt"{nim} r -b:cpp --hints:off --nimcache:{nimcache} --warningAsError:ProveInit {file}"
-    check execCmdEx(cmd) == ("witness\n", 0)
-
   block: # further issues with `--backend`
-    let file = testsDir / "misc/mimportcpp.nim"
+    let file = testsDir / "misc/mbackend.nim"
     var cmd = fmt"{nim} doc -b:cpp --hints:off --nimcache:{nimcache} {file}"
     check execCmdEx(cmd) == ("", 0)
     cmd = fmt"{nim} check -b:c -b:cpp --hints:off --nimcache:{nimcache} {file}"
     check execCmdEx(cmd) == ("", 0)
+    # issue https://github.com/timotheecour/Nim/issues/175
+    cmd = fmt"{nim} c -b:js -b:cpp --hints:off --nimcache:{nimcache} {file}"
+    check execCmdEx(cmd) == ("", 0)
+
+  block: # some importc tests
+    # issue #14314
+    let file = testsDir / "misc/mimportc.nim"
+    let cmd = fmt"{nim} r -b:cpp --hints:off --nimcache:{nimcache} --warningAsError:ProveInit {file}"
+    check execCmdEx(cmd) == ("witness\n", 0)