diff --git a/ast/parser.go b/ast/parser.go
index c24bbb505ac..f9f0e5aebab 100644
--- a/ast/parser.go
+++ b/ast/parser.go
@@ -729,6 +729,9 @@ func (p *Parser) parseRules() []*Rule {
 				next.Head.Args[i].Value = Var(p.genwildcard())
 			}
 		}
+		if hasIf {
+			next.Head.keywords = append(next.Head.keywords, tokens.If)
+		}
 		setLocRecursive(next.Head, loc)
 
 		rules = append(rules, &next)
@@ -743,6 +746,7 @@ func (p *Parser) parseElse(head *Head) *Rule {
 	rule.SetLoc(p.s.Loc())
 
 	rule.Head = head.Copy()
+	rule.Head.generatedValue = false
 	for i := range rule.Head.Args {
 		if v, ok := rule.Head.Args[i].Value.(Var); ok && v.IsWildcard() {
 			rule.Head.Args[i].Value = Var(p.genwildcard())
diff --git a/ast/parser_test.go b/ast/parser_test.go
index 2bd84d28aa8..37e416387c6 100644
--- a/ast/parser_test.go
+++ b/ast/parser_test.go
@@ -1409,6 +1409,26 @@ p := "foo" if {
 } else := "bar" if {
 	input.x == 2
 } else := "baz" if input.x == 3
+else := "qux"`,
+		},
+		{
+			note: "no else body (value assignment, but not on primary head) (regression test for #6364)",
+			module: `package test
+import rego.v1
+p if {
+	input.x == 1
+} else := "baz" if input.x == 3
+else := "qux"`,
+		},
+		{
+			note: "`if` keyword used before else body (value assignment, but not on primary head) (regression test for #6364)",
+			module: `package test
+import rego.v1
+p if {
+	input.x == 1
+} else := "bar" if {
+	input.x == 2
+} else := "baz" if input.x == 3
 else := "qux"`,
 		},
 		{
@@ -1517,6 +1537,256 @@ p.q[x] { x = input.x}`,
 import rego.v1
 default allow := false`,
 		},
+		{
+			note: "function, value assignment, no body",
+			module: `package test
+import rego.v1
+f(x) := x`,
+		},
+		{
+			note: "function, value assignment, body, with if",
+			module: `package test
+import rego.v1
+f(x) := x if {
+	x == 1
+}`,
+		},
+		{
+			note: "function, value assignment, body, no if",
+			module: `package test
+import rego.v1
+f(x) := x {
+	x == 1
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
+		{
+			note: "function, no value assignment, body, with if",
+			module: `package test
+import rego.v1
+f(x) if {
+	x == 1
+}`,
+		},
+		{
+			note: "function, no value assignment, body, no if",
+			module: `package test
+import rego.v1
+f(x) {
+	x == 1
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
+		{
+			note: "function, else without body, value assignment",
+			module: `package test
+import rego.v1
+f(x) := x if {
+	x == 1
+} else := 42`,
+		},
+		{
+			note: "function, else without body, value assignment only on else (regression test for #6364)",
+			module: `package test
+import rego.v1
+f(x) if {
+	x == 1
+} else := 42`,
+		},
+		{
+			note: "function, else with body and if, value assignment",
+			module: `package test
+import rego.v1
+f(x) := x if {
+	x == 1
+} else := 42 if {
+	x == 2
+}`,
+		},
+		{
+			note: "function, else with body and if, no value assignment",
+			module: `package test
+import rego.v1
+f(x) if {
+	x == 1
+} else if {
+	x == 2
+}`,
+		},
+		{
+			note: "function, else with body and no if, value assignment",
+			module: `package test
+import rego.v1
+f(x) := x if {
+	x == 1
+} else := 42 {
+	x == 2
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
+		{
+			note: "function, else with body and no if, no value assignment",
+			module: `package test
+import rego.v1
+f(x) if {
+	x == 1
+} else {
+	x == 2
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
+		{
+			note: "function, else with body and no if, value assignment on primary head",
+			module: `package test
+import rego.v1
+f(x) if {
+	x == 1
+} else := 42 {
+	x == 2
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
+		{
+			note: "function, else with body and no if, value assignment on else",
+			module: `package test
+import rego.v1
+f(x) := x if {
+	x == 1
+} else {
+	x == 2
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
+		{
+			note: "function, multiple else with body, no if on last else, value assignment",
+			module: `package test
+import rego.v1
+f(x) := x if {
+	x == 1
+} else := 1 if {
+	x == 2
+} else := 42 {
+	x == 2
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
+		{
+			note: "function, multiple else with body, no if on last else, value assignment on primary head",
+			module: `package test
+import rego.v1
+f(x) := x if {
+	x == 1
+} else if {
+	x == 2
+} else {
+	x == 2
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
+		{
+			note: "function, multiple else with body, no if on last else, value assignment on first else",
+			module: `package test
+import rego.v1
+f(x) if {
+	x == 1
+} else := 1 if {
+	x == 2
+} else {
+	x == 2
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
+		{
+			note: "function, multiple else with body, no if on last else, value assignment on last else",
+			module: `package test
+import rego.v1
+f(x) if {
+	x == 1
+} else if {
+	x == 2
+} else := 42 {
+	x == 2
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
+		{
+			note: "function, multiple else with body, no if on first else, value assignment",
+			module: `package test
+import rego.v1
+f(x) := x if {
+	x == 1
+} else := 1 {
+	x == 2
+} else := 42 if {
+	x == 2
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
+		{
+			note: "function, multiple else with body, no if on first else, value assignment on primary head",
+			module: `package test
+import rego.v1
+f(x) := x if {
+	x == 1
+} else {
+	x == 2
+} else if {
+	x == 2
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
+		{
+			note: "function, multiple else with body, no if on first else, value assignment on first else",
+			module: `package test
+import rego.v1
+f(x) if {
+	x == 1
+} else := 1 {
+	x == 2
+} else if {
+	x == 2
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
+		{
+			note: "function, multiple else with body, no if on first else, value assignment on last else",
+			module: `package test
+import rego.v1
+f(x) if {
+	x == 1
+} else {
+	x == 2
+} else := 42 if {
+	x == 2
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
+		{
+			note: "function, multiple else with body, no if on any else, value assignment",
+			module: `package test
+import rego.v1
+f(x) := x if {
+	x == 1
+} else := 1 {
+	x == 2
+} else := 42 {
+	x == 2
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
+		{
+			note: "function, multiple else with body, no if, value assignment",
+			module: `package test
+import rego.v1
+f(x) := x {
+	x == 1
+} else := 1 {
+	x == 2
+} else := 42 {
+	x == 2
+}`,
+			expectedErrors: []string{"rego_parse_error: `if` keyword is required before rule body"},
+		},
 	}
 
 	for _, tc := range tests {