diff --git a/src/cmd/compile/internal/gc/lex.go b/src/cmd/compile/internal/gc/lex.go
index d9ba9b210b..cf41c40964 100644
--- a/src/cmd/compile/internal/gc/lex.go
+++ b/src/cmd/compile/internal/gc/lex.go
@@ -1434,6 +1434,11 @@ casedot:
 	}
 
 caseep:
+	if importpkg == nil && (c == 'p' || c == 'P') {
+		// <mantissa>p<base-2-exponent> is allowed in .a/.o imports,
+		// but not in .go sources.  See #9036.
+		Yyerror("malformed floating point constant")
+	}
 	cp.WriteByte(byte(c))
 	c = getc()
 	if c == '+' || c == '-' {
@@ -1442,7 +1447,7 @@ caseep:
 	}
 
 	if !yy_isdigit(c) {
-		Yyerror("malformed fp constant exponent")
+		Yyerror("malformed floating point constant exponent")
 	}
 	for yy_isdigit(c) {
 		cp.WriteByte(byte(c))
diff --git a/test/fixedbugs/issue9036.go b/test/fixedbugs/issue9036.go
new file mode 100644
index 0000000000..283159e74a
--- /dev/null
+++ b/test/fixedbugs/issue9036.go
@@ -0,0 +1,29 @@
+// errorcheck
+
+// Copyright 2015 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Expects to see error messages on "p" exponents.
+
+package main
+
+import "fmt"
+
+const (
+	x1 = 1.1    // float
+	x2 = 1e10   // float
+	x3 = 0x1e10 // integer (e is a hex digit)
+	x4 = 0x1p10 // ERROR "malformed floating point constant"
+	x5 = 1p10   // ERROR "malformed floating point constant"
+	x6 = 0p0    // ERROR "malformed floating point constant"
+)
+
+func main() {
+	fmt.Printf("%g %T\n", x1, x1)
+	fmt.Printf("%g %T\n", x2, x2)
+	fmt.Printf("%g %T\n", x3, x3)
+	fmt.Printf("%g %T\n", x4, x4)
+	fmt.Printf("%g %T\n", x5, x5)
+	fmt.Printf("%g %T\n", x6, x6)
+}