diff --git a/cmd/oracle/main.go b/cmd/oracle/main.go
index c69d6721cb..77af07e0d0 100644
--- a/cmd/oracle/main.go
+++ b/cmd/oracle/main.go
@@ -27,11 +27,9 @@ import (
 	"code.google.com/p/go.tools/oracle"
 )
 
-// TODO(adonovan): use a format that permits spaces in filenames, and
-// doesn't require shell quoting.
 var posFlag = flag.String("pos", "",
 	"Filename and offset or extent of a syntax element about which to query, "+
-		"e.g. 'foo.go 123-456', 'bar.go 123'.")
+		"e.g. foo.go:123-456, bar.go:123.")
 
 var modeFlag = flag.String("mode", "",
 	"Mode of query to perform: callers, callees, callstack, callgraph, describe.")
diff --git a/cmd/oracle/oracle.el b/cmd/oracle/oracle.el
index 7b64a851a4..50e5830356 100644
--- a/cmd/oracle/oracle.el
+++ b/cmd/oracle/oracle.el
@@ -75,11 +75,14 @@ result."
   (if (string-equal "" go-oracle-scope)
       (go-oracle-set-scope))
   (let* ((filename (file-truename buffer-file-name))
-         (pos (if (use-region-p)
-                  (format "%s-%s"
-                          (1- (go--position-bytes (region-beginning)))
-                          (1- (go--position-bytes (region-end))))
-                (format "%s" (1- (position-bytes (point))))))
+         (posflag (if (use-region-p)
+                      (format "-pos=%s:%s-%s"
+                              filename
+                              (1- (go--position-bytes (region-beginning)))
+                              (1- (go--position-bytes (region-end))))
+                    (format "-pos=%s:%s"
+                            filename
+                            (1- (position-bytes (point))))))
          ;; This would be simpler if we could just run 'go tool oracle'.
          (env-vars (go-root-and-paths))
          (goroot-env (concat "GOROOT=" (car env-vars)))
@@ -89,7 +92,7 @@ result."
       (erase-buffer)
       (insert "Go Oracle\n")
       (let ((args (append (list go-oracle-command nil t nil
-                                (format "-pos=%s %s" filename pos)
+                                posflag
                                 (format "-mode=%s" mode))
                           (split-string go-oracle-scope " " t))))
         ;; Log the command to *Messages*, for debugging.
diff --git a/cmd/oracle/oracle.vim b/cmd/oracle/oracle.vim
index 68c16584c7..526e2d53ed 100644
--- a/cmd/oracle/oracle.vim
+++ b/cmd/oracle/oracle.vim
@@ -29,7 +29,7 @@ set errorformat+=%f:%l.%c-%*[0-9].%*[0-9]:\ %m
 func! s:RunOracle(mode) abort
   let s:pos = line2byte(line("."))+col(".")
   let s:errfile = tempname()
-  let s:cmd = printf("!%s -mode=%s '-pos=%s %d' %s >%s",
+  let s:cmd = printf("!%s -mode=%s -pos=%s:%d %s >%s",
     \ s:go_oracle, a:mode, bufname(""), s:pos, s:scope, s:errfile)
   execute s:cmd
   execute "cfile " . s:errfile
diff --git a/oracle/oracle.go b/oracle/oracle.go
index 37f95ccb5b..c366e60154 100644
--- a/oracle/oracle.go
+++ b/oracle/oracle.go
@@ -21,6 +21,8 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"strconv"
+	"strings"
 	"time"
 
 	"code.google.com/p/go.tools/go/types"
@@ -222,25 +224,43 @@ func ptrAnalysis(o *oracle) pointer.CallGraphNode {
 	return root
 }
 
-// parseQueryPos parses a string of the form "file pos" or file
-// start-end" where pos, start, end are decimal integers, and returns
-// the extent to which it refers.
+func parseDecimal(s string) int {
+	if s, err := strconv.ParseInt(s, 10, 32); err == nil {
+		return int(s)
+	}
+	return -1
+}
+
+// parseQueryPos parses a string of the form "file:pos" or
+// file:start-end" where pos, start, end are decimal integers, and
+// returns the extent to which it refers.
 //
 func parseQueryPos(fset *token.FileSet, queryPos string) (start, end token.Pos, err error) {
 	if queryPos == "" {
 		err = fmt.Errorf("no source position specified (-pos flag)")
 		return
 	}
-	var filename string
-	var startOffset, endOffset int
-	n, err := fmt.Sscanf(queryPos, "%s %d-%d", &filename, &startOffset, &endOffset)
-	if n != 3 {
-		n, err = fmt.Sscanf(queryPos, "%s %d", &filename, &startOffset)
-		if n != 2 {
-			err = fmt.Errorf("invalid source position -pos=%q", queryPos)
-			return
-		}
+
+	colon := strings.LastIndex(queryPos, ":")
+	if colon < 0 {
+		err = fmt.Errorf("invalid source position -pos=%q", queryPos)
+		return
+	}
+	filename, offset := queryPos[:colon], queryPos[colon+1:]
+	startOffset := -1
+	endOffset := -1
+	if hyphen := strings.Index(offset, "-"); hyphen < 0 {
+		// e.g. "foo.go:123"
+		startOffset = parseDecimal(offset)
 		endOffset = startOffset
+	} else {
+		// e.g. "foo.go:123-456"
+		startOffset = parseDecimal(offset[:hyphen])
+		endOffset = parseDecimal(offset[hyphen+1:])
+	}
+	if startOffset < 0 || endOffset < 0 {
+		err = fmt.Errorf("invalid -pos offset %q", offset)
+		return
 	}
 
 	var file *token.File
diff --git a/oracle/oracle_test.go b/oracle/oracle_test.go
index 98bd6836e7..17bb670d30 100644
--- a/oracle/oracle_test.go
+++ b/oracle/oracle_test.go
@@ -167,7 +167,7 @@ func doQuery(out io.Writer, q *query) {
 	buildContext.GOPATH = "testdata"
 	err := oracle.Main([]string{q.filename},
 		q.verb,
-		fmt.Sprintf("%s %d-%d", q.filename, q.start, q.end),
+		fmt.Sprintf("%s:%d-%d", q.filename, q.start, q.end),
 		/*PTA-log=*/ nil, capture, &buildContext)
 
 	for _, line := range strings.Split(capture.String(), "\n") {